What are the 3 main divisions of the digestive tract?
1. Oral Cavity
2. Tubular Parts
3. Associated Glands
At a basic level, what 2 processes make up digestion?
1. Breakdown of food (physically and chemically)
2. Absorption of nutrients
What are the 4 main parts of the oral cavity?
1. Lips
2. Teeth
3. Oral Mucosa
4. Tongue
What differentiates the oral mucosa of the gums and hard palate from the rest of the oral mucosa?
OM of gums and hard palate is keratinised: called masticatory mucosa.
The rest is called the lining mucosa
What is a lamina propria?
Loose connective tissue depp to epithelium of the mucosa. Rich in blood vessels and nerves, often glandular with many fenestrated capillaries.
Why does the tongue have 3 perpendicular layers of striated muscles?
Allow movement in any 3D direction.
What are the names of the posterior liymph nodules of the tongue?
Palatine and Lingual tonsils
What is contained within the papillae of the tongue?
Taste buds
What are the 4 main layers of the tubular digestive tract?
1. Mucosa
2. Submucosa
3. Muscularis Externa
4. Serosa/Adventitia
What components make up the mucosa of the tubular digestive tract?
1. Epithelium
2. Lamina Propria: a folded loose connective tissue that the epithelium rests on, often glandular with many fenestrated capillaries.
3. Muscularis Mucosae: Allows for movement of mucosa independent from rest of GI tract.
What are the 4 functions of the mucosa of the tubular digestive system
1. Primary Line of Defence: Physical barrier between interior of body and exterior, prevents free diffusion of foreign substances into body.
2. Secondary Line of Defence: Gut Associated Lymphatic Tissue (GALT)
3. Secretion (e.g. Mucous, HCl, Enzymes, Horm
What tissue makes up the submucosa of the tubular digestive tract?
Dense Irregular Connective Tissue
What are the 3 functions of the submucosa of the tubular digestive tract?
1. Support and Attachment
2. Contain blood & lymph vessels
3. Contain Meissner's Plexus of the enteric nervous system to innervate the muscularis mucosae
What is the role of Meissner's Plexus?
Innervate the muscularis mucosae.
Where is Meissner's Plexus found?
Submucosa of the tubular digestive tract.
What layers of muscle are found in the muscularis of the tubular digestive tract, and why is it arranged in this way?
Inner layer of circular bundles of smooth muscle, out layer of longitudinal bundles of smooth muscle.
This arrangement is key to enabling peristalsis, wave-like contractions of the GI tract.
What are the 3 main functions of the muscularis of the tubular digestive tract?
1. Peristalsis (wave-like contractions) accomplished by having an inner layer of circular and outer layer of longitudinal bundles of smooth muscle.
2. Segmentation: form sphincters between parts of the GI tract (e.g. pylorus between stomach and duodenum)
Where is Auerbach's Plexus found?
Between the smooth muscle layers of the muscularis of the tubular digestive tract.
What is the role of Auerbach's Plexus?
Innervate the muscularis of the tubular digestive tract.
Compare and contrast the serosa and adventitia of the tubular GI tract.
Serosa: visceral peritoneum, a simple squamous epithelium with small amounts of dense irregular connective tissue that covers organs of the digestive tract. Secretes a lubricating fluid at surfaces so organs can move freely and not stick to each other or
Describe the structure of the mucosa of the esophagus and why it has this structure?
Non-keratinized squamous epithelium that is thick to provide protection during swallowing (especially in animals like snakes that swallow prey whole).
What is found in the submucosa of the esophagus?
Lymphatic nodules and mucous glands to provide lubrication for swallowing.
How is the muscularis of the esophagus divided down its length?Why?
Top 1/3: Mostly striated
Mid 1/3: Mix of smooth and striated
Bottom 1/3: Mostly smooth
This allows for voluntary control of initiation of swallowing from the oral cavity, but autonomic control takes over as it enters the rest of the GI tract.
What are the primary functions of the esophagus?
1. Swallowing
2. Protection
Where is the adventitia vs serosa of the esophagus?
Adventitia: near upper region, diffuse with surrounding tissue.
Serosa: Only present near stomach.
What are the three major regions of the stomach and where are they located?
Cardia: Near heart, where esophagus opens into.
Fundus: Main 'body' of the stomach
Pylorus: End that opens into duodenum
What is secreted by the glandular pits found in the mucosa of the stomach?
What is the total mixture called?
Mucous
HCl
Enzymes
Hormones
--Mixed together with food, this becomes chyme.
What substance is secreted by surface mucosal cells of the stomach?
Mucinogen: a viscous milky substance that becomes mucous when mixed with chyme.
What is secreted by Mucous Neck Cells of the stomach?
A more-water soluble form of mucous.
What is absorbed in the stomach?
Water
Glucose
Salts
Some drugs
--Overall, simpler, smaller molecules.
What are the layers (from superficial to deep) of the mucosa of the stomach?
Epithelium and gastric pits
Lamina Propria
Muscularis Mucosa
What is the structure of the submocosa of the stomach?
Folded into rugae -- folds of the stomach that help increase surface area.
What features are found in the submucosa of the stomach?
Blood & lymphatic vessels
Meissner's Plexus
How are muscles arranged in the muscularis of the stomach?
Inner strands of oblique muscle
Middle layer of circular muscles
Outer longitudinal muscles
What type of cell composes the majority of glands in the cardiac and pylroric regions of the stomach?
Mucous cells -- irregular with flat basal nuclei and apically clear cytoplasm (because it stores mucinogen)
What are the functions of the mucous secreting cardiac and pyloric glands of the stomach?
1. Protect against abrasion
2. Protect against acid
Beyond mucopolysaccharides, what is secreted by cardiac and pyloric glands of the stomach to help protect against the acidity of chyme?
Bicarbonate -- neutralises acid
What are the four regions of a fundic gland of the stomach? What cells are found in each?
1. Gastric pit: surface mucous cells
2. Isthmus: stem cells that replicate and differentiate (high turnover rate in stomach)
3. Neck: Parietal & mucous neck cells
4. Base: Chief cells, parietal cells, enteroendocrine cells.
Where are chief (zymogenic) cells found in the stomach, and what is their role here?
Found in the base of fundic glands, secrete pepsinogen which is conveted to pepsin in the acidic conditions of the stomach lumen -- proteolytic enzyme that breaks down ingested proteins.
Describe the appearance of the cytoplasm of Chief cells of fundic gland, and why it looks this way.
Basal: slightly basophilic due to abundant rough endoplasmic reticulum
Apical: Full of secretory vesicles (zymogen granules), filled with pepsinogen, can appear red in preparation.
Where are parietal (oxyntic) cells found in the stomach, and what is their role here?
Spherical/pyramidal cells with a central spherical nucleus and acidophilic or clear cytoplasm that contains canaliculi, found in the neck and base region of fundic glands.
Secretes HCl to acidify the stomach for chemical digestion, activation of pepsinoge
What enzymes regulate secretions of parietal cells in the fundic glands?
Gastrin: increases secretion
Secretin: decreases secretion
Where are enteroendocrine cells found in the stomach, and what is their role here?
Pyramidal cells with a central spehrical nucleus and basal domain filled with hormonal vesciles, found in the Neck and Base of fundic glands.
Secretes gastrin and ghrelin into circulation through the lamina propria: DOES NOT SECRETE INTO THE LUMEN OF THE
In the stomach, what is an 'open' enteroendocrine cell?
One where the apical domain is exposed to the lumen of its gastric gland. It has many chemoreceptors here to monitor contents of the glandular lumen, and secrete a particular hormone accordingly.
What are the three regions of the small intestines?
1. Duodenum
2. Jejunum
3. Ileum
What are the 5 main functions of the small intestines?
1. Transport food unidirectionally
2.Finish digestion/breakdown of food via more digestive secretions
3. Hormonal secretions for regulation of digestion
4. Absorption of final digestion projects
5. Immunological protection (barriers)
What are the 3 surface specialisations of the small intestines?
1. Pilicae Circulares
2. Villi
3. Microvilli
What are pilicae circulares?
Macroscopic circular folds of the surface of the large and small intestines to increase surface area.
As they are at surface, they represent folds of the mucosa.
Describe the villi of the intestines: what are they?
Small microscopic folds of the mucosal surface to increase intestinal surface areas -- they allow more cells to be in contact with the lumen.
What are microvilli?
Very small microscopic projections off the apical domain of epithelial cells to increase surface area.
What glands are found in the mucosa of the small intestines and what is their role?
Crypts of Lieberkuhn
Participates in absorption.
What glands are found in the submucosa of the small intestines and what is their role?
Brunner's glands -- found in the submucosa of the duodenum.
Has an alkaline secretion (pH = 8-9) to neutralise the acidic chyme coming from the stomach through the pylorus.
What are the enterocytes of the small intestines? What is their function?
Columnar absorptive cell that form the epithelium of the intestinal mucosa.
Apical surface has a brush-like border of microvilli and prominent terminal bars forming tight junctions.
Function is to absorb nutrients, including ions, water, amino acids, suga
How much do the microvilli of enterocytes increase their absorptive capacity by?
600 times greater than without.
Describe goblet cells of the small intestine. What do they look like, what do they do?
Goblet-shaped, with an ovoid/spherical basal nucleus. Cytoplasm is filled with mucinogen granules.
Found throughout the intestinal mucosal epithelium, especially in glands. Apical cytoplasm is full of mucinogen granules, making it appear clear and giving
Describe paneth cells of the small intestine. What do they look like, what do they do?
Pyramidal cells found near the base of intestinal glands of some mammals. Basal spherical nucleus with intensely acidophilic cytoplasm.
Role is to regulate bacterial flora, by secreting antibacterial lysozymes and defensins and through phagocytosis.
This
What hormones are secreted by the enteroendocrine cells of the small intestines?
1. Cholecystokinin
2. Gastric Inhibitory Peptide
3. Motilin
What is the role of Cholesystokinin secreted by enteroendocrine cells of the small intestines?
- Stimulates exocrine pancreas (enzymes) and gall bladder secretions.
- Inhibits gastric secretion of HCl.
- Inhibits motility.
What is the role of Gastric Inhibitory Peptide secreted by enteroendocrine cells of the small intestines?
- Stimulates insulin secretion (endocrine) from the pancreas
- Inhibits gastric secretions
What is the role of motilin secreted by enteroendocrine cells of the small intestines?
- Increases gut motility
Describe the Intermediate Cells of the small intestine -- what is their structure and function?
Stem cells found in the lower half of intestinal glands -- irregular and columnar shape.
They replicate and differentiate into other mucosal and epithelial cells -- 4-7 day turnover for surface intestinal cells.
Describe the M-Cells (Microfold Cells) of the small intestine -- what is their structure and function?
Cells that overlie Peyer's Patches (especially prevalent in the Ileum) and other lymphatic nodules (GALT).
They feature apical microfolds creating deep pocket-like reecesses.
Function: Antigen transport cell:
- Endocytosis transport of antigens to immune
What is notable about the lamina propria of the small intestines?
Loose areolar connective tissue of the mucosa that contains a lot of GALT (including Peyer's patches -- a lymphatic nodule especially prevalent in the ileum) and other diffuse lymphoid tissue.
The lamina propria in villi contain lots of immune cells (lymp
What four components make up the large intestines?
1. Cecum & Appendix
2. Colon: 4 sections
- Ascending
- Transverse
- Descending
- Sigmoid
3. Sigmoid Colon
4. Anal Canal
What are unique features of hte large intestines?
- No villi on mucosa
- Muscularis exterrna shows prominent bands of smooth muscle: the Taenia Coli (TC)
- Haustra Coli (HC): Visible bulges on the external surface
- Omental Appendices: Fatty projections of the serosa
What cells are found in the large intestine?
1. Columnar Absorptive Cells: Rich in sodium pumps to create an osmotic gradient to drive water reabsorption.
2. Mucous Goblet Cells: Lubrication for feces
3. Enteroendocrine cells: less abundant than small intestine, involved in nutrient reabsorption.
4.
How does abundance of mucous goblet cells vary between the small and large intestines
Much more abundant in large intestine -- more lubrication needed
Beyond nutrient absorption, what main feature does the large intestine lack?
No specific immune features: no paneth cells, peyer's patches, or nodules.
No regulation of gut microbiota.
Why are there many more enteroendocrine cells in the small intestine than large?
These regulate nutrient absorption, which occurs much more in the small than large intestine.
What are the four main functions of the large intestine?
1. Absorb water & ions.
2. Secrete mucous to lubricate feces.
3. Minimal amounts of digestion.
4. Movement and excretion of feces.
What is the pyloric caeca?
Finger-like projections that stick out of the pyloric region of the GI tract in fish. Precise purpose/function is unknown.
What is the spiral valve?
A bulge of the intestine of fish that is filled with a spiral structure through which chyme must travel. This is an alternative adaptation to intestinal elongation to prolong the time chyme spends in the intestines for digestion and absorption.
What is a diagastric stomach?
Adaptation of foregut fermenters, multichambered stomach. They chew, swallow, regurgitate, then chew some more, and pass contents between stomach. Prolongs time food is digested as they have a diet of plant matter that is very difficult to digest.
Better
What adaptations allow hindgut fermenters to consume difficult-to-digest plant matter?
Cecum and large intestines (especially ascending colon) are greatly enlarged. Cecum acts as a 'fermentation vat', full of microbiota that can break down plant matter.
Better large amounts of low quality food.
What is an avian crop, and what function does it serve?
Digestive adaptation, like a second storage stomach to keep extra food to regurgitate for young, or store for later.
What is an avain gizzard, and what function does it serve?
Digestive adaptation, extra pouch where bird can swallow and store rough substances like gravel to help with mechanical digestion of food (since they don't really chew).
What are the 3 main pairs of salivary glands?
1. Parotid
2. Submandibular
3. Sublingual
What are the 3 main components of saliva?
1. Water
2. Proteins (Mucin, a-amylase, lingual lipase, lysozyme, IgA -- mucous lubricates, enzymes commence chemical digestion and immune components)
3. Salts (CaPO4, KCl, NaCl)
What are the functions of saliva?
- Moisten the oral mucosa and food
- Medium to chemically stimulate taste buds (dissolve chemical components of food so they are available for detection).
- Buffer oral cavity
- Commence chemical digestion with a-amylase & lingual lipase
- Control bacteri
What is the lober duct of a salivary gland?
A large central duct that travels through the main body of the gland and branches into smaller interlobular ducts off into each lobe of the gland. This continues to branch until it becomes the smallest unit, the acinus duct.
What is the basic secretory unit of a salivary gland? What components make up this structure?
Salivon:
1. Acinus (where secretion actually occurs)
2. Intercalated Duct
3. Striated Duct
4. Excretory duct
What structures compose the lobules of a salivary gland?
Acini (= grapes in latin)
Where are myoepithelial cells located in salivary glands and what is there role?
At the base of acini and within intercalated ducts. They help pump secreted product towards excretory ducts.
What are the different types of acini of salivary glands, and what do they secrete?
1. Serous acini: secrete proteins (amylase, lysozome, etc.)
2. Mucous acini: secrete mucinogen
3. Mixed acini: contain both serous and mucous cells
What types of acini are found in the parotid gland?
Only serous acini.
What types of acini are found in the submandibular gland?
Mixed acini, but proportionally more serous cells.
What types of acini are found in the sublingual gland?
Mixed acini, but proportionally more mucous cells.
Describe the epithelium of intercalated ducts of the salivon.
Simple cuboidal
Describe the epithelium of striated ducts of the salivon.
Columnar epithelium with basal invaginations:
Role of basal invaginations is to increase surface area for reabsorption of water and Na+, K+ HCO3- secretions.
How do ducts of the salivon influence the final product secreted by the gland?
Basal invaginations of simple columnar epithelium of Striated Ducts allow for reabsorption of water and Na+, K+ HCO3- secretions.
Describe the blood supply/input to the liver?
Blood enters through the portal canal.
~75% of incoming blood comes through the portal vein -- this is deoxygenated blood that has already passed through capillary beds of the GI tract, and is now entering the liver to be filtered before the products abso
What is a liver acinus?
The smallest metabolic unit of a liver -- can be thought of as a somewhat arbitrary diamond shape between the central veins of two hepatic lobules encompassing the functional cells within them.
Can be divided into 3 distinct functional zones based on prox
How are the different zones of a hepatic acinus affected by fluctuations in oxygen or toxin concentration?
Zone 1 is closest to the edge of a hepatic lobule, so the first to receive oxygen, and so is resilient to oxygen fluctuations. However, it is also the first to receive toxins, and so are more affected by toxin levels.
Zone 3 is closest to the central vein
What structures define a hepatic (classic) lobule?
Hexagonal structure with triad portal canals at vertices, and central vein in middle. Parenchyma radiates out from central vein.
Blood travels in towards the central vein through sinusoids, where it is filtered by hepatocytes and Kupffer cells. Bile trave
What is a portal lobule of the liver?
A triangular area surrounding a triad canal. Three central veins make the vertices.
This organisation emphasizes the exocrine bile secreting function of the liver.
What are three ways to structurally organise the liver.
1. Hepatic (Classic) lobule: hexagonal lobule with parenchyma radiating from central vein to triad portal canals at vertices.
2. Portal Lobule: Triangular area around central triad portal canal where bile collects, with central veins of classic lobules ma
What does parenchyma mean?
Functional portion of tissue (as opposed to structural).
Where in a hepatic lobule does direct exchange between blood and hepatocytes occur?
Sinusoidal space of Disse.
What structural adaptation is observed in hepatocytes to increase their surface area for blood filtration?
Microvilli
Why is the cytoplasm of hepatocytes slightly basophilic?
Full of many peroxisomes, organelles involved in detoxifcation via oxidase, catalase, & alcohol dehydrogenase.
What is the main role of hepatocytes?
Filter blood passing through the sinusoids of a hepatic lobule.
Why do hepatocytes have tight junctions between each other?
Form bile caniculi to secrete bile into that is eventually taken to the bile ducts of the triad portals.
What enzymes stimulate bile production inhepatocytes?
Cholecytokinin
Gastrin
There are others, generally enzymes secreted by endocrine organs.
What role do hepatocytes play in glucose metabolism?
They take in glucose the body has just absorbed in the intestine, and convert it to glucose-6-phosphate, which allows it to be stored as glycogen.
They can also reverse this process and break down stored glycogen to glucose that is released to the bloodst
What plasma proteins are released by hepatocytes, and what is their role?
Albumins, transferrins, VLD, lipoproteins.
In general, these are transport proteins, especially for lipid transfer -- hydrophobic substances cannot freely diffuse through blood, so they need to be carried by proteins.
What does secretion of bile & salts by hepatocytes accomplish?
Aids in waste disposal -- e.g. primary component of bile is bilirubin, which is recovered from recycled red blood cells.
Also helps in nutrient absorption in the intestines.
What are the endocrine functions of hepatocytes?
Conversion of vitamins and hormones from precursor to active form. Secretion of activated hormones.
What are all the functions of hepatocytes?
1. Filtration and detoxification of blood
2. Glucose Metabolism (Glycogen storage and breakdown)
3. Production of plasma proteins (especially lipid transporters)
4. Detoxification and excretion of wastes (e.g. drugs, urea, other toxins, etc.)
5. Secretion
What is the role of endothelial cells of hepatic lobules?
Line sinusoids, with a thin, discontinuous, and incomplete basal lamina -- very open to allow blood access to space of disse.
What are Kupffer cells? What is their role and where are they found?
Fixed macrophages of hepatic lobules that help blood filtration by phagocytosisis of pathogens that go past in sinusoids.
What are Ito cells? What is their role and where are they found?
Cells that store vitamin A, found in hepatic lobules between hepatocytes.
What functional structures are the lobules of the pancreas organised into?
Acini connected by ducts, like salivary glands.
Where do the ducts of the exocrine pancreas eventually release into?
Duodenum
What is the structure of a pancreatic acinus?
5-8 pyramidal acinar cells surroudnign centroacinar cells that lead to an intercalated duct.
Describe the appearance of pancreatic acinar cells and why they look this way?
Spherical and basal nucleus, large and polygonal in shape. Cytoplasm is slightly basophilic but apical domain faces into acinus and is filled very acidophilic zymogen granules containing proenzymes.
What is secreted by the acini of the exocrine pancreas?
Proenzymes to aid in digestion:
- Proteolytic enzymes to digest proteins (e.g. trypsinogen
- Nucleases to digest nucleic acids (DNAse, RNAse)
- Amylolytic enzymes to digest carbohydrates (e.g. amylase)
- Lipases to digest lipids into fatty acids & glycero
What is one way that the intercalated ducts of the pancreas modifies acinar secretion, and why does it do this?
Secretes bicarbonate to help with neutralising chyme coming into duodenum.
Summarise the exocrine functions of the pancreas.
1. Produce and secrete proenzymes -- various digestive enzymes in inactive form (proteolytic, nuclease, amylolytic, lipase)
2. Secrete bicarbonate to help neutralise chyme in duodenum.
What are Islets of Langerhans?
Endocrine regions of the pancreas dispersed throughout the exocrine parenchyma.
Describe structural elements of islets of langerhans.
Irregular mass of cell distributed throughout the pancreas, heavily vascularised by fenestrated capillaries to take up products to circulation.
What type of stain can distinguish the different cells of the islets of langerhans?
Mallory-Azan stain.
What are the cell types found in the Islets of Langerhans? What are their rough proportions, and what is the main role of each?
1. B-Cells: 60~70% of islet, secrete insulin
2. a-Cells: 15-20% of islet, secrete glucagon
3. D-Cells: 5-10% of islet, secrete somatostatin.
What is the role and appearance of Beta-Cells of the Islets of Langerhans?
Full of brownish-orange granules containing insulin: hormone that stimulates glucose uptake by tissues of muscles, the liver, adipose tissue, decreases overall blood-glucose levels.
What is the role and appearance of alpha-Cells of the Islets of Langerhans?
Full of red granules containing glucagon: a hormone that increases blood-glucose levels by activating gluconeogenesis and glycogenolysis in the liver.
What is the role and appearance of D-Cells of the Islets of Langerhans?
Blue staining cytoplasm, secrete somatostatin which slows down the overall digestive process by:
- Inhibiting glucagon & insulin production
- Inhibiting the exocrine pancreas
- Inhibiting rate of grastric contractions
- Inhibiting intestinal blood flow an
How did immunohistochemistry help discover the cells and roles of the endocrine pancreas?
Endocrine pancreas = islets of langerhans. The cells here cannot be differentiated in an H&E stain, but can by Mallory-Azan stain -- however this is an uncommon staining method. Immunohistochemistry helped provide more clarity and detail to the cells of t
What structures make up the conducting portions of the respiratory system?
1. Nasal Cavity
2. Pharynx
3. Larynx
4. Trachea
5. Bronchus
6. Bronchioles
What are the functions of the conducting portions of the respiratory system?
1. Filter particulates (e.g. mucous rich lining catches things like dust and pollen. Beating cilia on apical end of cells facing lumen helps push this up and out)
2. Moisten air
3. Regulate temperature of air
4. Olfaction & vocalisation.
What are the structures of the respiratory portion of the respiratory system?
Lungs: Divided into:
- Respiratory Bronchioles
- Alveolar Ducts
- Alveolar Sacs
- Alveolus
What are the four main structural features of the nasal cavity? What are their functions?
1. Vestibule: traps large particles, lines opening
2. Median septum & Conchae Bony Projections: Turbulent precipitation: Creates a turbulent air flow against surfaces to force air to be filtered
3. Lamina Propria of nasal mucosa: highly vascularised heat
What is turbulent precipitation and how is it accomplished?
Turbulent airflow into the nasal cavity as a result of the median septum and conchae (bony nasal projections) -- this turbulent flow forces air against surfaces of the nasal cavity so it is filtered.
What are the four cell types of the nasal mucosa?
1. Olfactory cells
2. Supporting cells
3. Basal cells
4. Olfactory (Bowman's) glands
What are olfactory cells of the nasal cavity?
Neural sensory cells -- feature apical cilia covered in olfactory receptors.
Long axons go straight to olfactory bulb in brain.
Each olfactory cell produces only one type of olfactory receptor.
What is the role of supporting cells of the nasal mucosa?
Produce odorant-binding proteins to help olfactory cells detect odorants?
What are the basal cells of the nasal cavity?
Stem cells to regenerate cells at surface of nasal mucosa, as these are most at risk of damage.
What is produced by the Olfactory (Bowman's) glands found in the nasal mucosa?
Serous secretion to trap and serve as a solvent for odoriferous substances.
What is the structure of cartilage in the trachea?
Anterior border supported by C-rings of hylaine cartilage.
Posterior border lies against esophagus, supported by fibroelastic connective tissue and smooth muscle connecting the cartilage rings together.
Describe the 4 layers of the trachea.
1. Mucosa, containing epithelium and lamina propria invaded by BALT.
2. Submucosa composed of loose connective tissue, mucous glands, and lymphatic tissue
3. Cartilage/bone/smooth muscle layer of supporting tissues
4. Adventitia, not a distinct serosa def
What type of epithelium makes up the upper conducting portions of the respiratory tract? What cells are found within it?
Pseudostratified columnar epithelium with a thick basement membrane.
1. Ciliated columnar cells: act as a muscociliary elevator
2. Mucous (goblet) cells
3. Basal stem cells
4. Enteroendocrine cells: secrete hormones to regulate airway and vascular caliber
What composes the serosa of lungs?
Pleura membrane, two-layers of serous membrane
What is the pleural cavity?
Fluid filled space between the visceral and parietal pleura around the lungs. Fluid is derived from blood.
Allows friction-free movement of blood.
What respiratory components are found in the lungs?
Conducting:
- Bronchi
- Distributing Bronchioles
Respiratory:
- Respiratory bronchioles
- Alveolar ducts
- Alveolar sacs
- Alveoli
Describe the blood supply to the lungs? Why do they receive blood from two different systems?
Pulmonary supply:
Carries deoxygenated blood from the right ventricle of the heart through the pulmonary artery to the alveolar capillaries where gas exchange occurs and blood is reoxygenated before returning to the left atrium via the pulmonary vein. Thi
Describe the structure of the cartilage of the bronchi? How is it different than that of the trachea?
Irregular plates of hyaline cartilage instead of incomplete rings.
Describe the layers of the bronchi and the features of each.
1. Mucosa: epithelium with reticular and elastic fibres in the lamina propria
2. Muscularis: bundles of smooth muscle
3. Submucosa: glandular and lymphoid tissue
4. Cartilate: complete rings early on that degrade into incomplete rings.
5. Adventitia: no s
What are the main distinguishing features of bronchioles?
No cartilage plates, but prominent smooth muscle.
Respiratory bronchioles contain both thicker-walled sections full of smooth muscles and Clara cells, as well as thinner-walled recesses for gas exchange.
What are Clara cells? Where are they found and what is their function?
Non-ciliated cells in the epithelium of respiratory bronchioles, secrete an anti-adhesive surface lipoprotein that prevents walls from sticking to each other to avoid airway collapse.
What are alveoloar ducts?
Thin-walled tubes off of respiratory bronchioles that lead into alveolar sacs.
What are the main features of the alveoli?
- Thin walled polyhedral chamber that is the primary site of gas exchange
- Surrounded by a capillary network
- Organised into alveolar sacs
- Separated from one another in sacs by alveolar septum that contains many functional components.
What are the three main components of the alveolar septum?
1. Alveolar epithelium
2. Connective tissue with elastic fibers:
- Prevent collapse (implosion)
- Prevents explosion (resists air pressure)
- Medium for movement of alveolar macrophages
3. Capillary endothelium
What distinguishes the thick and thin portions of the alveolar septum?
Thick: all three septal layers together (epithelium, connective portion, endothelium)
Thin: Only epi & endothelium, no connective tissue portion.
What is the purpose of the thin portion of the alveolar septum? What is found there?
Minimal air-blood barrier for gas exchange.
Contains:
- Alveolar epi & endothelial cells
- Fused basal lamina
- Layer of surfactant on alveolar lumen side to prevent sticking and collapse.
What cells are found in the alveolar septum?
1. Type 1 Alveolar cells: Squamous cells composing 40% of cells but covering 95% of surface area.
2. Endothelial cells of capillaries
3. Type 2 alveolar cells: cuboidal/globular cells composing 60% of cells but covering only 5% of surface area. Form tight
What cells of the alveoli secrete surfactant?
Type 2 alveolar cells of the septum.
What features of the respiratory system are conserved across vertebrates?
- Thin blood-air barrier
- High surface area
- Highly vascularised moist surface.
What are the special adaptations of avian respiration?
Unidirectional air flow -- so air passes over respiratory surfaces one way during both inhalation & exhalation.
Accomplished by air sacs that make up ~15% of body volume, and system of parabronchi running through lungs.
Compare & contrast the respiratory surfaces of mammals, avians, and non-avian reptiles.
Mammals: alveoli, blind-ended sacs
Avians: Exchange surface from parabronchi, air flows unidirectionally over respiratory surfaces due to system of air sacs.
Non-avian reptiles: Structure analagous to single mammalian alveolus, lumen divided by septum whe
What structures form the integumentary system?
Skin + specialised structures (glands, nails, claws, hair, scales, feathers, etc.)
What are the two main layers of skin?
1. Epidermins: stratified epithelium that is often squamous and keratinised.
2. Dermis: Loose & dense irregular connective tissue, often quite thick
Can also be a hypodermis, lowest layer composed mostly of adipose tissue.
What are the 6 functions of the integumentary system?
1. Physical barrier to physical, chemical, and biologic agents.
2. Homeostasis, especially thermoregulation.
3. Sensation
4. Endocrine functions (e.g. Vitamin D synthesis)
5. Excretion (e.g. sweat, sebum)
6. Immunologic function & surveillance
What are keratinocytes: where are they found and what is their function?
Predominant cell type of the epidermis.
Start from the deepest layer and travel superficially as mature. Continually produce and store keratin as they grow until they die and cover the superficial epidermis with their protective keratinous husk.
What is the function of melanocytes? Where are they found?
Found in deep epidermis between keratinoctytes, with many branching processes between them. Produce the pigment melanin from tyrosine and transfer it to keratinocytes via their branching processes.
Melanin protects DNA from UV radiation.
What are Langerhan's Cells: where are they found and what is their function?
Found in the epidermis, feature a characteristic nucleus that has many indentations, and rod shaped body. Very prevalent, found between keratinocytes.
Part of the 'mononuclear phagocyte system': protect against infection via phagocytsis, then migrate to l
What are Merkel's Cells: where are they found and what is their function?
Found in deep basal epidermis near afferent sensory nerve terminals. Charecterised by dense neurosecretory granules,.
They act as a sensitive cutaneous mechanoreceptor.
What cell types are found in the epidermis?
1. Keratinocytes
2. Melanocytes
3. Langerhan's cells
4. Merkel's cells
What are the four layers of the epidermis?
1. Stratum Basale
2. Stratum Spinosum
3. Stratum Granulosum
4. Stratum Corneum
What features distinguish the stratum basale of the epidermis?
Bottom/deep/basal layer containing basal/stem cells
Hemidesmosomes anchor cells to the basal membrane.
What features distinguish the stratum spinosum of the epidermis?
The layers immediately superficial to the stratum basale: keratinocytes begin synthesizing keratin here.
The keratinocytes appear to have spinous processes on their surface, hence the name.
Neighbouring processes become linked by desmosomes
What features distinguish the stratum granulosum of the epidermis?
3rd epidermal layer.
Keratinocytes now have two main features:
Keratohyalin Granules: proteins that promote aggregation of keratin in cytoplasm
Lamellar bodies: lipid mixture that contributes to extracellular water barrier
What features distinguish the stratum corneum of the epidermis?
Outermost superficial layer. Quite thick where protection is needed, e.g. soles of feed.
Full of anucleate cornifed (packed full of keratin filaments) cells
Soft keratin: low sulfur content, found on skin surface
Hard keratin: high sulfur content, hair an
What distinguishes the keratin on the surface of the skin from that found in hair and nails?
Hard vs. soft keratin -- varies in amount of sulfur, to form disulfide bonds.
What eventually causes desmosomes between keratinocytes to degrade so dead ones are shed from skin?
Low pH triggers proteases that do this.
What are the 2 layers of the dermis?
1. Papillary layer: Composed of loose connective tissue rich in blood vessels and nerves. Marked by dermal papillae, invaginations between dermis and epidermis.
2. Reticular Layer: Charecterised by thick dense irregular collagen bundles
What composes the hypodermis?
Layers of adipose tissue, and sometimes striated muscle.
Panniculus adiposus: Adipose tissue layer, providing insulation and energy storage
Panniculus carnosus: Striated muscle layer, for things like facial expression.
What three segments compose a hair follicle?
1. Infundibulum: Surface to sebaceous gland
2. Isthumus: Sebaceous gland to insertion of arrector pili
3. Interior segment: contains hair bulb
What integumentary features develop from downgrowths of the epithelium?
Hair follicles
Sebaceous glands
Eccrine & apocrine sweat glands
What is the role of arrector pili muscles?
Small muscles in the skin that raise body hair and form goose bumps.
What are the epidermally derived parts of a hair bulb?
Medulla
Cortex
Cuticle
Root Sheath
What are the dermally derived parts of a hair bulb
Dermal/Hair papilla
Dermal Sheath
How does hair grow at a histological level?
Follicular bulge contains epidermal stem cells --these provide stem cells both for hair follicle matrix and sebaceous glands
Cells from the matrix that congtribute to the hair shaft become keratinised
Melanin pigments cause hair colour and are donated to
What two cell types are found in sweat glands?
Secretory cells, produce sweat
Myoepithelial cells, contract to pump out sweat
What is the structure and function of eccrine sweat glands?
Highly coiled and convoluted, independent of hair follicles, but open at surface.
Help with thermoregulation
What is the structure and function of apocrine sweat glands?
Highly coiled and convoluted, open at base of hair follicles. Wider lumen and darker cells than eccrine glands.
Found in axillary, mammary glands, and around genitalia.
Secretion varies with location, but in general secrete behaviourally relevant odours,
What are sebaceous glands?
Outgrowths of the external root sheaths.
They undergo holocrine secretion: whole cell dies and ruptures to release contents to infindibulum of hair follicle.
Release sebum: a waxy lipid secretion that coats hair and skin to help lubricate and waterproof i
Briefly describe the structure and formation of nails.
Epidermal specialisation of hard keratin.
Keritinasation occurs in nail matrix and nail root.
Lunula: region of active proliferaton/keritinisation
Eponychium (cuticle)/hyponychium: Thickened layers of epidermis between nail and skin.
How do the scales of repitiles vary with those of fish?
Reptilian scales are an epidermal adaptation, whereas fish scales are dermal and ossified.
What drives variation of the integumentary system across vertebrates?
Strategy for maintaining water balance and thermoregulation.
What are the two ways in which sensory organs are categorised?
Either by the origin of their stimulus or the energy to which they are sensitive.
What mechanoreceptors are found in skin?
Free nerve endings: fine touch and temperature
Pacinian corcpuscles: found in dermis, hypodermis, and pancreas, espeically in fingertips, respond to deep touch and pressure
Meissner's Corpuscles: Found in dermal papillae, respond to light touch
Ruffini's
What two types of photoreceptor cells are found in the eye?
Rods (general light sensitivity)
Cones (colour)
What are the three tissue layers of the eye?
1. Corneoscleral coat
2. Vascular coat: Choroid, ciliary body, iris
3. Retina
What 3 chambers make up the eye?
1. Anterior chamber
2. Posterior Chamber
3. Vitreous Chamber
What is the corneoscleral limbus?
Transition zone between cornea and sclera
What are the functions of the corneoscleral limbus?
1. Source of stem cells that maintain corneal epithelium.
2. Outflow of anterior chamber fluid (aqueous humour) via Canal of Schlemm
How many tissue layers make up the corneoscleral coat?
3 connective tissue layers
What are the 5 layers of the cornea, from superficial to deep?
1. Non-keratinising stratified epithelium
2. Bowman's membrane (basal lamina)
3. Stroma: regular dense connective tissue
4. Decemet's membrane (basal lamina)
5. Simple corneal epithelium: single layer of squamous cells allowing for metabolic exchange betw
What are the choroid layers of the vascular coat of the eye?
1. Chroiocapillary Layer: loose connective tissue with fenestrated capillaries that supply the retina
2. Lamina Vitrea (Brunch's Membrane): Thin layer between capillaries and pigment epithelium of membrane.
Transports nutrients to retina, and metabolic wa
What is the structure of the ciliary body of the eye? What does it do?
Ciliary muscle: adjusts lense
Ciliary process: vascular region covered by a two-layer columnar epithelium
Secretes the aqueous humour
Forms blood-aqeuous layer
Anchors lense through zonula fibres
Describe the three important structures of the iris.
Vascularised connective tissue stroma containing melanocytes.
Smooth muscles: constrictor (sphincter) and dilator pupilae musces, provide adaptation to ambient light
Pigment epithelium, gives eye colour -- without stroma, default eye colour is blue.
What are the 10 layers of the retina, from inner to outer (surface in vitreous chamber)
1. Retinal pigment epithelium
2. Rods & cones
3. Outer limiting membrane
4. Outer nuclear layer
5. Outer plexiform layer
6. Inner nuclear layer
7. Inner plexiform layer
8. Ganglion cell layer
9. Layers of optic nerve fibres
10. Inner limiting membrane
What is the function of the retinal pigment epithelium?
Blood-retina barrier, absorption of scattered light
What are the supporting neuroglial cells of the retina?
Muller's cells, cover the entire retinal surface
What are the conducting neurons of the retina?
Bipolar and ganglion cells
What are the association neurons of the retina?
Amacrine & horizontal neurons
What are three components of the lens of the eye?
1. Lens capsule: elastic basal lamina
2. Subcapsular epithelium
3. Lens fibres: crystalline proteins
What tissue composes the auricles/pinnae of the external ear?
Elastic cartilage
What is the role of the External Acoustic Meatus?
Conduct sound to the tympanic membrane.
Underlain by sebaceous and ceruminous glands.
Why does the tympanic membrane not repair well if damaged?
It is not very cellular
What three layers compose the tympanic membrane?
Epithelium of acoustic meatus
Radial and circular collagen fibres
Mucous membrane of middle ear
What connects the tympanic cavity of the ear to the pharynx?
Eustachian tube
What are the auditory ossicles?
3 bones in the middle ear that transmit and amplify the vibrations of the tympanic membrane. They are composed of the:
1. Malleus
2. Incus
3. Stapes
What is the tensor tympani?
A muscle attached to the stapes, helps attenuate ear against loud sounds.
What are the two main compartments of the inner ear?
1. Bony labyrinth, consisting of the: cochlea, vestibule, and semicircular canals
2. Membranous labyrinth, consisting of the: vestibular labyrinth within the semicircular canals (aids balance), and cochlear labyrinth
What specialised structures in the vestibular labyrinth of the ear contains sensory cells?
Semicircular canal ampulla: cupula of gelatinous materials that rest on the stereocilia of hair cells
What is the organ of corti?
A spiral sensory structure found within the cochlear labyrinth of the inner ear.
What membranes divide the inner ear into three compartments?
Vestibular membrane between scala vestibuli and scala media, and basilar membrane between scala media and scala tympani.
What cells are found on the Spiral Organ of Corti?
1. Supporting cells.
2. Hair cells
What is the tectorial membrane?
Membrane of collagen fibres that lies over the basilar membrane of the spiral organ of corti -- hair cells are attached to each, shearing between these membranes deflects the stereocilia of hair cells, allowing sensory detection of vibration of noise.
Why does the basilar membrane decrease in stiffness as it travels away from the oval window that the stapes beats against?
Allows for optimal responses to different frequency ranges along its length.
What are the 4 main functions of the kidneys?
1. Urine production (remove waste but preserve fluids & electrolytes)
2. Maintain acid-base balance
3. Regulate extracellular fluid
4. Endocrine activities (secrete EPO & renin. Hydroxylation of Vitamin D precurson)
What are the 4 main regions of the kidney?
1. Hilum
2. Capsule
3. Cortex
4. Medulla
What are lobes of the kidney divided into?
Medullary pyramids -- associated cortical tissue is in renal columns
What is found at the end of medullary pyramids?
Renal papilla
What is the path from a renal papilla to the bladder?
Renal papilla
Minor calyx
Renal pelvis
Ureter
What are the 2 portions of a nephron? What is the function of each?
1. Renal corpuscle: ultrafiltration of blood to produce primary urine
2. Tubule system: Conduction & processing of primary urine
What nephronic parts are found in the renal cortex?
Renal corpuscles and convoluted tubules
What nephronic parts are found in the medullary rays?
Extensions of the medullary collecting ducts, associated straight tubules
What nephronic parts are found in the renal medulla?
Straight tubules, collecting ducts, vasa recta
What nephronic parts are found in the renal papilla?
Most distal portion of collecting ducts, opening just above the minor calyx
What structures compose the renal corpuscle?
Glormeruls surrounded by Bowman's Capsule: a double-layered epithelium:
1. Parietal layer, simple squmous epithelial container
2. Visceral layer, complex filtration barrier
Between the layers is the urinary space where ultrafiltrate is received
What are the components of the triple barrier of the visceral layer of the renal corpuscle?
1. Endothelial cells of fenestrated glomerular capillaries
2. Thick glomerular basement membrane, provides a size- (only substances smaller than 70 kDa) and ion-selective barrier (restricts anion movement)
3. Podocyte cells: foot processes (pedicles) form
Where is the proximal tubule of a nephron found? What are its structural charecteristics and function?
Mainly found in cortex, has both convoluted and straight portion. Lumen has a brush border of microvilli
Absorbs Na+ and reabsorbs 65% of filtrate via osmotic gradient
Performs active transport of amino acids and sugars
Takes in large peptides via endocyt
What is the function of the proximal portion of the proximal tubule of a nephron: the thick descending limb?
Recover remaining glucose that escaped proximal convoluted tubule.
What is the function of thin descending limb of the proximal tubule of a nephron?
Reabsorption of water -- permeability is high to water and low to ions, leading to increased tubular osmolality
What is the function of thin ascending limb of the proximal tubule of a nephron?
Reabsorption of ions (Na+, Cl-, K+): highly permeable to ions but low to water, making surrounding interstitium hyperosmotic
What is the function of the distalportion of the proximal tubule of a nephron: the thick ascending limb?
Reabsorption of Ca2+ and Mg2+
Where is the distal convoluted tubule of a nephron found? What are its structural charecteristics and function?
Found in cortex.
Smaller diameter than proximal convoluted tubule, but not brush border in lumen.
Reabsorbs Na+ in exchange for K+ (regulated by aldosterone) and bicarbonate.
Secretes H+ to regulate pH
Where are the collecting tubules and ducts of a nephron found and what is their function?
Extend down medullary rays to the medullary pyramid.
Reabsorbs water, regulated by antidiuretic hormone leading to insertion of aquaporin channels.
Reabsorbs Na+ in exchange for K+, regulated by aldosterone
Secretes protons or bicarbonate as needed.
Why does the length of the loop of henle vary in mammals?
Depends on water regulation needs. A longer loop of henle allows for more water reabsorption and very concentrated urine.
Mammals like beavers that live in freshwater do not require this because freshwater is abundant.
Mammals like camels that live in des
What is the juxtoglomerular apparatus?
Region of the kidney where the distal convoluted tubules contact the vascular pole of the renal corpuscle.
3 specialised cell types:
1. Macula densa, small cells of distal convoluted tubule that are crowded with nuclei
2. Juxtaglomerular cells, modified m
Describe the urothelium.
Transitional epithelium of bladder. Contains rigid urothelial plaques on apical surface that forms a strong barrier to salts and water, and fold along hinge to help urine expand/contract.
What are the 3 tissue layers of the bladder and ureters?
1. Mucosa, featuring transitional epithelium and lamina propria
2. Muscularis with inner longitudinal and outer circular muscles
3. Adventitia composed of fibroelastic connective tisse
What structures make up the female reproductive system?
Ovaries
Uterus
Fallopian (uterine) tubes
Vagina
External genitalia
Mammary glands
What connecting peritoneum attaches the ovary to the uterus?
Mesovarium
What is the role of the infundibulum/fimbria of the uterine tube?
Collect oocyte after ovulation.
What are the two main structures of the ovary, and what is found in each region?
1. Cortex, containing ovarian follicles and stroma
2. Medulla containing loose connective tissue, blood/lymphatic vessles, and nerves
What are the endocrine and exocrine functions of the ovaries?
Endocrine: steroidogensis, produces and secretes estrogen and progesterone form follicles
Exocrine: cytogenic: gamete production/secretion.
What is the origin of germinal cells in the ovary?
Arise from yolk sac early in embryonic development and migrate to gonads to avoid differentiation.
What structure are follicular cells derived from?
Germinal epithelium
What are the three stages of follicle development, and what defines each?
1. Primordial follicle: oocyte surrounded by single layer of squamous follicular cells and outer basal lamina
2. Primary follicle: stratified cuboidal follicular cells, zona pellucida is clear space containing glycoproteins between follicular cells and oo
What is the role of the zona pellucida surrounding an oocyte?
Glycoproteins that bind spermatazoa to initiate acrosome reaction.
What are the features of the exterior of a mature graafian follicle?
Theca foliculi surround follicle:
Theca interna is highly vascular and produce androgens (estrogen precursor)
Theca externa are more fibrous and contain some smooth muscle.
What is the process of ovulation?
Luteinizing Hormone surge activates proteolytic enzymes that digest collagen in follicular wall and cause smooth muscles in theca externa to contract. Wall ruptures and oocyte surrounded by corona radiata is released.
What is luteinisation and what is its result?
After ovulation. luteinizing hormone results in theca lutin and granulosa lutein cells. These secrete progesterone and estrogen to prevent menstruation and maintain the endometrium of the uterus.
What is the corpus albicans?
Structure resulting from progessive degeneration of corpus luteum following pregnancy or menstruation.
Where does fertilisation occur?
Within the uterine tubes.
Describe the walls of the uterine tubes?
Highly folded mucosa, especially in ampulla.
Simple columnar epithelium consisting of both ciliated cells and non-ciliated peg cells
Ciliary movement helps move ovum/zygote
Muscularis (inner circular, outer longitudinal) drive peristalsis
Serosa is compos
What is the role of peg cells in the mucosa of uterine tubes?
Secrete nutritional fluids for the gametes and zygote
What 3 layers make up the wall of the uterus?
1. Endometrium, featuring a large mucosa with many mucous glands. Stratum functionale undergoes cyclic proliferation and menstruation
2. Myometrium, very large smooth muscle zone with 3 distinct layers
3. Perimetrium, outer serosal layer
What is the transformational zone of the cervix?
Abrupt transition from epithelium of uterus to new type
Why are there many mucous glands found in the cervix?
Facilitate sperm transport
What does pyknosis of the nucleus of a cervical pap smear mean and what does it indicate?
Pyknosis is enlarged nucleus, and can be a sign of cervical cancer.
What are the endocrine and exocrine functions of the testes?
Endocrine: Leydig cells produce testosterone, stimulated by luteinizing hormone
Exocrine: Cytogenic, produce spermatazoa -- stimulated by follicle stimulating and luteinizing hormones
What connective tissues are found around the testes?
1. Tunica Vaginalis, mesothelium surrounding testis
2. Tunica albuginea, dense connective tissue capsule
3. Connective tissue septa projecting into tests, defining ~250 lobules
4. Mediastinum testis, inward projection of tunica albuginea for entry exit of
Where are spermatazoa produced within the testes?
Seminiferous tubules
Where are leydig cells found and what is their role?
Found in tissue stroma between seminiferous tubules of testis.
Eosinophilic cytoplasm filled with lipid vacuoles to synthesize testosterone from cholesterol in elaborate smooth ER.
What are the 2 main elements of seminiferous tubules?
1. Sertoli cells that cover many other cells to provide support and nutrients
2. Spermatogenic cells that are targets of Follicle Stimulating Hormone and Testosterone to produce spermatozoa.
What cells define the blood-testis barrier in the seminiferous epithelium, to isolate spermatogenic cells from the immune system?
Sertoli cells
What is secreted by sertoli cells to promote maturation of spermatogenic cells?
Androgen-binding protein to concentrate testosterone within the seminiferous tubules.
What are myoid cells in the lamina propria of seminiferous tubules?
Contractile cells to allow for peristalsis
What is the general process of spermatogenesis?
Spermatogonia are stem cells covering the basal lamina of the seminiferous tubules.
They mature into primary spermatocytes that undergo DNA replication, then meiosis
Secondary spermatocytes are the first haploid meiotic product, and undergo secondary meio
What are the regions of the seminiferous tubules?
Refe testis
Efferent ductules
Ductus epididymis
Ductus deferens
Ejaculatory ducts
Urethra
What are the glandular regions of the male reproductive tract?
Seminal vesicles and prostate glands
Discharge secretions into the ejaculatory ducts and prostatic urethra
Describe the epithelium of the ductus epididymis.
Pseudostratified, principal cells have sterocilia
What are the functions of the ductus epididymis?
1. Absorption
2. Secretion
3. Phagocytosis
4. Storage of Spermatazoa
How many muscle layers are found in the ductus epididymis, and what is their role?
3 layers.
Provides peristalsis to power ejaculation.
What are the three regions of the male urethra?
1. Prostatic: transitional epithelium from bladder
2. Membranous: between prostate gland and base of penis -- pseudostratified or columnar epithelium
3. Penile: transitions from stratified columnar to stratified squamous, ending in stratified keratinised
What is the structure and function of seminal vesicles?
Pair gland surrounded by fibrous coat with smooth muscle and highly folded mucosa with simple to columnar pseudostratified epithelium
Fructose-rich secretion nourishes spermatazoa
What is the general structure and function of the prostate gland?
Fibromuscular stroma that contracts during ejaculation. Columnar or cuboidal glandular epithelium.
Secretes fibrinolysis and serine protease to liquify semen.
What are 3 general charecteristics of endocrine glands?
1. Formed of aggregates of epithelioid cells embedded within connective tissue
2. Ductless, discharge directly into ECM
3. Richly vascularised
What are four classes of endocrine hormones?
1. Peptides
2. Steroids
3. Amines
4. Eicosanoids from arachidonic acid
What are the 2 regions of the pituitary gland and what is the embryonic origin of each?
1. Adenohypophysis, from oral ectoderm (Rathke's pouch)
2. Neurohypophysis from neural tube
What are the 3 regions of the adenohypophysis?
1. Pars distalis
2. Pars tuberalis
3. Pars intermedia
How is secretion from the adenohypophysis regulated?
Hypothalamic neurosecretory hormones -- transported to anterior lobe via portal vessles
What makes up the hypophysial portal system?
Reticular network derived from capsule surrounding parenchyma. Clusters/cords of cells are separated by sinusoids.
What are the 3 main categories of cells of the adenohypophysis?
1. Chromophobic cells, containing depleted or inactive secretory vesicles
- Chromophilic cells:
2. Acidophils, either somatotropes (secrete growth hormone) or lactotropes (secrete prolactin)
3. Basophils that are iether thyrotropes (secrete Thryroid Stimu
What are the 2 main regions of the neurohypophysis?
1. Pars nervosa
2. Infundibulum
What is the role of the neurohypophysis?
Not an endocrine gland -- instead terminals of neurosecretory neurons lie in the hypothalamus -- neurohormones are delivered here via axonal transport from storage in the posterior pituitary lobe.
Excitation of neurosecretory hormone elicits release from
What are herring bodies?
Accumulation of neurosecretory vesicles found in the axon terminals in the neurohypophysis/hypothalamus
What are the two main structures of the adrenal glands, and their embryonic origins and secretions?
1. Cortex, derived from mesoderm, secretes steroids
2. Medullam, derived from neuroectoderm, secretes catecholamines
What are the 3 zones of the adrenal cortex, and what is secreted by each?
1. Zona Glomerulosa: curved clusters of columnar cells that secrete aldosterone stimulated by angiotensin 2
2. Zona fasciulta: long cords of cuboidal cells that are stimulated by ACTH to secrete cortisol
3. Zona reticularis: bundles/groups of cells with n
What hormones are secreted by the adrenal medulla?
Catecholamines: epinephrine and norepinephrine
What is the function of epinephrine/norepinephrine?
1. Glycogenolysis
2. FFA mobilisation
3. Increased blood pressure
4. Blood shunting towards muscles
5. Increased heart/respiratory rate
How is the medulla of adrenal glands innervated?
By preganglionic sympathetic nerves so the medullary cells themselves are post-ganglionic
What neurotransmitter triggers release of catecholamines by adrenal medullary cells?
Acetycholine
What embryonic tissue is the thyroid gland derived from?
Pharyngeal epndoderm
What cells are present in a thyroid follicle?
1. Follicular cell
2. Parafollicular cell
What are the dual functions of a thyroid follicular cell?
1. Thyroglobulin secretion into the follicle colloid for storage
2. Thyroglobulin reabsorption and processing into T4-Thyroxine and T3-triiodothyronin and release of those into blood
Overall regulates development, growth, metabolism, and body heat generat
What is the role of parafollicular thyroid cells?
Secrete calcitoning to lower blood Ca++ by supressing osteoclast activity and inhibiting Ca++ reabsorption in gut and kidney
What 2 cells compose the parathyroid gland?
1. Chief/principal cells
2. Oxyphil cells -- more with age but function unknown
What is the role of chief/principal cells of the parathyroid gland?
Increase blood Ca++ levels by secreting parathyroid hormone: stimulates production of osteoclasts and reabsorption of Ca++ in gut and kidneys.
How are cells arranged in the pineal gland?
Pinealocytes: found in clumps and cords
Interstitial/Glial cells are like astrocytes
What are the functions of the pineal gland?
Secrete melatonin to:
Regulate circadian rhythm by regulating clock gene activity in the superchiasmatic nucleus
Seasonal synchronisation of:
1. Gonadotropin Releasing Hormone & prolactin
2. Coat Growth
3. Camouflage colouring.