Ch 18: Endocrine System

Hormones, simplified

Chemicals secreted by glands.

Pineal gland, simplified

Regulates daily rhythms. Think melatonin in the middle of the night. Situated in the brain. Third eye.

Thymus gland, simplified

On top of heart. Involved in immune system - makes T-lymphocytes. More important in immunity in younger years.

Thyroid gland, simplified

Controls metabolism. Increased T3 and T4 speeds up metabolism and vice versa. On throat.

Pituitary Gland, simplified

Posterior - secretes oxytocin and ADH
Anterior - secretes a number of hormones w/diff. effects. (Controls things from thyroid to endorphins)

Homeostasis and Endocrine system

Hugely connected. Blood and calcium levels, for ex. regulated by the glands. Also blood glucose control, which are controlled by islets of Langerhans.

Diabetes and Endocrine, simplified

Too much glucose in urine - so, glucose we can't use.
2 types:
Type 1 - autoimmune disorder where cells in pancreas are attacked and insulin is not made correctly
Type 2 - less to do w/ insulin and more to do with cells, which are not sure what to do with

Adrenal glands

Control quick response.
2 types:
Medulla: involved in flight or fight response... adrenaline
Adrenal cortex: long term stress and its effects.


A mediator molecule - released in one part of the body but regulates the activity of cells in other parts of the body.

How hormones circulate

Most enter interstitial fluid and then the bloodstream. The circulating blood delivers hormones to cells throughout the body. They exert their effects by binding to receptors on/in target cells.

Endrocine vs. Nervous System control

Endocrine - slower and longer acting. Acts on virtually all types of body cells.
Nervous - faster, briefer and acts on specific muscles and glands.

Exocrine glands - definition

Secrete their products into ducts that carry the secretions into body cavities, into the lumen of an organ or to the otuer surface of the body.

Exocrine glands - example

Sudoriferous, sebaceous, mucous and digestive glands.

Endocrine glands - definition

Secrete their products into the interstitial fluid surrounding the secretory cells rather than into ducts. From the inters. fluid, hormones diffuse into capillaries and blood carries them to target cells throughout the body.

Endocrine glands - example

Pituitary, thyroid, parathyroid, adrenal and pineal glands.

Hormone receptors

Hormones influence their target cells by chemically binding to these.

Target cells

Only these cells for a given hormone have receptors that bind and recognize that hormone.


If a hormone is present in excess, the number of target cell receptors will decrease. This is called...


If a hormone is deficient, the number of receptors may increase, making a target cell more sensitive to a hormone. This is called...

Circulating hormones

Refers to most hormones. They pass from the secretory cells that make them into interstitial fluid and then into the blood.

Local hormones

Act locally on neighboring cells or on the same cell that secreted them without first entering the bloodstream.


Local hormones that act on neighboring cells


Local hormones that act on the same cell that secreted them.

2 chemical classes of hormones

Lipid-soluble and water-soluble

Lipid-soluble hormones

- steroid hormones
- thyroid hormones
- nitric oxide

Water-soluble hormones

- amine hormones
- peptide hormones and protein hormones
- eicosanoid hormones

Hormone transport in the blood

Most water-soluble hormones circulate in the water blood plasma in a free form whereas most lipid-soluble hormone molecules are bound to transport proteins.

Transport proteins - location of synthesization

Synthesized in the liver

Transport proteins - three functions

1. They make lipid-soluble hormones temporarily water soluble, thus increasing their solubility in blood
2. They retard passage of small hormone molecules through the filtering mechanism in the kidneys, thus slowing the rate of hormone loss in the urine.

Free fraction

0.1 - 10% of the molecules of a lipid-soluble hormone are not bound to a transport protein. This fraction diffuses out of capillaries, binds to receptors and triggers responses.

Action of lipid-soluble hormones

Lipid-soluble steroid hormones and thyroid hormones affect cell function by altering gene expression.

Action of water-soluble hormones

Water-soluble hormones alter cell function by activating plasma membrane receptors, which elicit production of a second messenger that activates various enzymes inside the cell.

Three types of effects of hormonal interactions

1. Permissive
2. Synergistic
3. Antagonistic

Permissive effect

The action of some hormones on target cells require a simultaneous or recent exposure to a second hormone. The second hormone is said to have this effect.

Synergistic effect

The effect when two hormones acting together is greater or more extensive than the effect of each hormone acting alone.

Antagonistic effect

The effect when one hormone opposes the actions of another hormone.

Control of hormone secretion

- release of most hormones occurs in short bursts, with little or no secretion between bursts.
Regulated by:
1. signals from the nervous system
2. chemical changes in the blood
3. other hormones

Relationship btwn hypothalamus and pituitary

Hypothalamus is master of pit.
- Hypothalamus is major link between nervous and endocrine systems




Pea-shaped structure that lies in the hypophyseal fossa of the sella turcica of the sphenoid bone.
- attached to the hypothalamus by the infundibulum and has two anatomically and functionally separate lobes.


Attaches the hypothalamus and pituitary.

Anterior pituitary

aka adenohypophysis
- accounts for 75% of total weight of the gland

Two parts of anterior pit

1. pars distalis (larger portion)
2. parts tuberalis (forms a sheath around the infundibulum)

Posterior pituitary

aka neurohypophysis
- contains axons and axon terminals of more than 10,000 neurons whose cell bodies are located in the supraoptic and paraventricular nuclei of the hypothalamus.

Two parts of posterior pit

1. pars nervosa (larger bulbar portion)
2. infundibulum

Anterior pit and release of its hormones

Secretes hormones that regulate a wide range of bodily activities.
- release of ant pit hormones is stimulated by releasing hormones and suppressed by inhibiting hormones.

Hypophyseal Portal system

The means through which hypothalamic hormones reach the anterior pituitary. Blood flows from capillaries in the hypothalamus into portal veins that carry blood to capillaries of the anterior pituitary.

Portal system

Blood flows from one capillary network into a portal vein and then into a second capillary network without passing through the heart.

Neurosecretory cells

Specialized neurons that synthesize the hypothalamic releasing and inhibiting hormones in their cell bodies and package the hormones inside vesicles, which reach the axon terminals by axonal transport.

The anterior pituitary hormones

1. hGH - Human growth hormone
2. TSH - Thyroid-stimulating hormone
3. FSH - Follicle-stimulating hormone
4. LH - Luteinizing hormone
5. PRL - Prolactin
6. ACTH - Adrenocoricotropic hormone
7. Melanocyte-stimulating hormone

Human Growth hormone

Stimulates liver, muscle, cartilage, bone and other tissues to synthesize and secrete insulinlike growth factors, which promote growth of body cells, protein synthesis, tissue repair, lipolysis and elevation of blood glucose concentration.

Thyroid-stimulating hormone

Stimulates synthesis and secretion of thyroid hormones by thyroid gland

Follicle-stimulating hormone

In females, initiates development of oocytes and induces ovarian secretion of estrogens. In males, stimulates testes to produce sperm.

Luteinizing hormone

In females, stimulates secretion of estrogens and progesterone, ovulation and formation of corpus luteum. In males, stimulates testes to produce testosterone.


Together with other hormones, promotes milk secretion by the mammary glands.

Adrenocorticotropic hormone

Stimulates secretion of glucocorticoids by adrenal cortex.

Melanocyte-stimulating hormone

Exact role in humans in unknown by may influence brain activity; when present in excess, can cause darkening of skin.

Control of secretion by anterior pituitary

Regulated in two ways:
1. Neurosecretory cells in hypothalamus secrete five releasing hormones, which stimulate secretion of anterior pituitary hormones and two inhibiting hormones, which suppress secretion of anterior pituitary hormones
2. Negative feedb

Posterior pituitary

Does not synthesize hormones. Instead stores and releases them.

The posterior pituitary hormones

1. Oxytocin
2. Antidiuretic hormone


Neurosecretory cells of hypothalamus secrete this in response to uterine distention and stimulation of nipples.
- Stimulates contraction of smooth muscle cells of uterus during childbirth
- stimulates contraction of myoepithelial cells in mammary glands t

Antidiuretic hormone

aka vasopressin
- Neurosecretory cells of hypothalamus secrete ADH in response to elevated blood osmotic pressure, dehydration, loss of blood volume, pain or stress
- release inhibited by lower blood osmotic pressure, high blood volume and alcohol.
- cons

Thyroid gland

- located just inferior to the larynx
- composed of R and L lateral lobes, connection by an isthmus.
- normal mass: 30g
- highly vascularized
- receives 80 - 120 ml of blood/minute

Thyroid follicles

Microscopic spherical saces that make up most of the thyroid gland
- made up of follicular cells that secrete the thyroid hormones


One of the thyroid hormones.
-aka tetraiodothyronine or T4 (because it contains 4 atoms of iodine)


One of the thyroid hormones.
- aka T3 because it contains three atoms of idoine.

Parafollicular cells

aka C cells
- lie between thyroid follicles
- produce calcitonin which helps to regulate calcium homeostasis.

Formation, storage and release of thyroid hormones

Thyroid gland is the only endocrine gland that stores its secretory product in large quantities, normally approx 100-day supply.
- hormones are synthesized from iodine and tyrosine within thyroglobulin.
- they are transported in the blood bound to plasma

Actions of T3 and T4

Increase basal metabolic rate, stimulate synthesis of proteins, increase use of glucose and fatty acids for ATP production, increase liplysis, enhance cholesterol excretion, accelerate body growth and contribute to development of the nervous system.

Actions of Calcitonin

Lowers blood levels of Ca2+ and HPO4 by inhibiting bone resorption by osteoclasts and by accelerating uptake of calcium and phosphates into bone matrix.

Parathyroid glands

Normally 4 of them
- embedded in the posterior surface of the thyroid gland.
- composed of small rounds masses of tissue.

Two types of cells of parathyroid glands

Both are types of epithelial cells
1. Chief (principal) cells - produce parathyroid hormone. Are the more numerous.
2. Oxyphil cells - function unknown.

Parathyroid hormone

Regulates the homeostasis of calcium, magnesium and phosphate ions by increasing blood calcium and magnesium levels and decreasing blood phosphate levels.
- secretion is controlled by the level of calcium in the blood.


Synthesized by the kidneys, this is the active form of Vit D. Parathyroid hormed stimulates the kidneys to synthesize this.

Adrenal glands

A pair of glands, each of which lies superior to each kidney
- have a flattended pyramidal shape
- 3 -5cm in height

Two regions of the adrenals

Are structurally and functionally different
1. adrenal cortex: large and peripherally located. Comprises 80 - 90% of the gland.
2. adrenal medulla: small and centrally located

Adrenal cortex

Secretes mineralocorticoids, glucocorticoids and androgens.


One of the secretions of the adrenal cortex.
- increase sodium and water reabsorption
- decrease potassium reabsorption


One of the secretions of the adrenal cortex.
- promote protein breakdown, gluconeogenesis and lipolysis
- help resist stress
- serve as anti-inflammatory substances


One of the secretions of the adrenal cortex.
- stimulate the growth of axillary and pubic hair
- aid the prepubertal growth spurt
- contribute to libido

Adrenal medulla

Secretes epinephrine and norepinephrine, which are released during stress and produce effects similar to sympathetic responses.


Is both an endocrine gland and an exocrine gland.
- a flattened organ located in the curve of the duodenum
- consists of a head, a body and a talk.


Clusters of pancreatic cells
- produce digestive enzymes which flow into the gastrointestinal tract through a network of ducts

Pancreatic islets

1 - 2 million tiny clusters of endocrine tissue that are scattered among the exocrine acini
aka islets of Langerhans

Cell types in pancreatic islets

1. Alpha cells (A cells) - constitute about 17% of pancreatic islet cells. Secrete glucagon.
2. Beta cells (B cells) - constitute about 70% of pancreatic islet cells. Secrete insulin.
3. Delta cells (D cells) - constitute about 7% of pancreatic islet cell


The organs that produce gametes


Paired oval bodies located in the female pelvic cavity
- produce several steroid hormones including 2 estrogens and progesterone, which regulate the menstruate cycle, maintain pregnancy and prepare the mammary glands for lactation


Also produced by ovaries
- inhibits secretion of FSH


A hormone produced by the ovaries and placenta during pregnancy
- increases flexibility of the pubic symphysis during pregnancy
- helps dilate uterine cervix during labour and delivery.


Oval gonads that lie in the scrotum.
- produce testosterone, a male sex hormone
- also produce inhibin


Regulates production of sperm and stimulates the development and maintenance of male secondary sex characteristics

Pineal gland

A small endocrine glad attached to the roof of the third centrical of the brain at the midline.
- consists of pinealocytes


Masses of neuroglia and secretory cells


Secreted by pineal gland
- an amine hormone derived from serotonin


Located behind the sternum between the lungs.
- plays a role in immunity.

Stress response (or general adaptation syndrome)

A sequence of bodily changes that occur under a variety of stressful conditions.
- controlled mostly by hypothalamus.
Occurs in three stages:
1. flight or fight response
2. a slower resistance reaction
3. exhaustion

Flight or fight response

Initiated by nerve impulses from the hypothalamus to the sympathetic division of the autonomic nervous system
- mobilizes the body's resources for immediate physical activity.
- brings huge amounts of glucose and oxygen to the organs that are most active

Resistance reaction

Second stage in the stress response.
A longer lasting response.
- releases a series of hormones that help the body continue fighting a stressor long after the fight or flight response dissipates.


Third stage in the stress response.
Prolonged exposure to high levels of cortisol and other homones involves in the resistance reaction causes wasting of muscle, suppression of the immune system, ulceration of the gastrointestinal tract and failure of pan

Stress and disease

Stress can lead to particular diseases by temporarily inhibiting certain components of the immune system.

Pituitary dwarfism



- Hypersecretion of hGH during childhood
- Abnormal increase in the length of long bones.
- Grows to be very tall; body proportions are about normal.


-Hypersecretion of hGH during adulthood.
- At this point, hGH cannot produce further lengthening of long bones, b/c epiphy. plate is closed, the bones of the hands, feet, cheeks and jaws thicken and other tissues enlarge.
- also, eyelids, lips, tongue and

Diabetes Insipidus

Associated with dysfunction of the posterior pituitary
- Due to defects in antidiuretic hormone receptors or an inability to secrete ADH.
- Treatment involves hormone replacement, usually for life.

Thyroid gland disorders

Among the most common endocrine disorders
- affect all major body systems

Congenital hypothyroidism

Hyposecretion of thyroid hormones that is present at birth
- Must be treated promptly to avoid devastating consequences


Produced by adult hypothyroidism
- Hallmark is edema that casuses the facial tissues to swell and look puffy.
- Slow heart rate, low body temp, sensitivity to cold, dry hair and skin, muscular weakness, lethargy and tendency to gain weight easily.
- 5x mo

Graves disease

Most common form of hyperthyroidism
- 7-10x more common in females
- An autoimmune disorder in which the person produces antibodies that mimic the action of TSH
- These antibodies continually stimulate the thyroid gland to grow and produce thyroid hormone


An enlarged thyroid gland.
May be associated with hyperthyroidism, hypothyroidism and euthyroidism (normal TSH).

Cushing's syndrome

Produced by hypersecretion of cortisol by the adrenal cortex.
- Caused by a tumour either of the adrenal glad or another tumor that secretes adrenocorticotropic hormone.
- Characterized by breakdown of muscle proteins and redistribution of body fat: spind

Addison's disease

Hyposecretion of glucocorticoids and aldosterone
- aka 'chronic adrenocortical insufficiency')
- due to autoimmune disorders in which antibodies cause adrenal cortex destruction or block binding of ACTH to its receptors.
- Symptoms only appear once 90% of

Diabetes Mellitus

The most common endocrine disorder
- Caused by an inability to use or produce insulin
- Insulin in unavailable to aid transport of glucose into body cells, so blood glucose level is high and glucose spills into the urine (glucosuria).
- Hallmarks: excessi


Decreased blood glucose level
- Excess insulin stimulates too much uptake of glucose by body cells.
- The resulting hypoglycemia stimulates the secretion of epinephrine, glucagon and human growth hormone.
- Results in anxiety, sweating, tremor, increased