Systems Involved in Excretion
(Elimination of metabolic waste)
Urinary system
_____urine
Respiratory system
____________breathing
Digestive system
_______feces
Integumentary system
_____sweat
Functions of the Urinary System
Excretion of metabolic wastes
Regulation of fluid and electrolyte balance
Regulation of blood acidity-alkalinity or (pH)
Regulation of blood volume & pressure by Renin
Production of Erythropoietin hormone that stimulate RBC formation in the bone marrow
Ac
kidney
filter blood and produce urine
urether
transport urine to urinary bladder
urinary bladder
stores urine until eliminated
urethra
is tube for elimination of urine
sheaths kidney
renal capsule
outer region
renal cortex
inner region with 8-18 renal pyramids
renal medulla
apex or tip of renal pyramid
renal papila
cortical tissue between the pyramids
renal column
minor calyx
receives urine from renal papilla
major calyx
collects urine from two or more minor calyces
renal pelvis
collects urine from all major calyces
ureter
urine from renal pelvis to bladder
THE NEPHRON
Microscopic filtering units of kidneys composed of renal corpuscle, renal tubules and a blood supply
Called functional units - that make urine
About 1 million per kidney
Mostly in renal cortex with some tubules extending into renal pyramids of medulla
Renal corpuscle
Loops of capillaries called glomerulus
Double layered Bowman's capsule surrounds glomerulus
renal tubules
Proximal convoluted tubule (PCT) connects to Bowman's capsule
Loop of Henle with descending and ascending limbs
Distal convoluted tubule (DCT) is last part of nephron
DCT of several nephrons connect to a collecting duct (CD)
Four processes required for urine formation
. Filtration of water and solutes from the glomerulus blood into the Bowman's capsular space
Tubular Reabsorption of useful substances from renal tubules filtrate into the glomerulus blood
Tubular Secretion of waste products from the glomerulus blood into
FILTERATION
High glomerular capillary hydrostatic pressure of about 60 mmHg forces water and solutes through the filtration membrane which is formed by the glomerular capillary wall and visceral layer of Bowman capsule
Water and many different solutes pass from glomerulus blood into
bowmans capsule
Resulting fluid in capsular space called
filtrate
Filtrate contains
Metabolic wastes such as urea and uric acid that must be eliminated in the urine
Useful substances such as water, organic nutrients and electrolytes that must be kept
renal blood flow (RBF
Amount of blood flow through kidneys in one minute
About 1200 mL/minute
Around 10% of RBF becomes a filtrate
glomerular filtration rate (GFR)
Amount of filtrate formed in one minute
About 120 mL/minute
what is regulation of gfr done by
by controlling amount of glomurelar blood flow
what increases gfr
Dilation of afferent arteriole and constriction of efferent arteriole
auto regulation
Regulation of GFR by the juxstaglomerular / macula densa apparatus
neural regulation
Sympathetic nervous system stimulation during exercise or in circulatory shock decreases GFR
hormonal regulation
By Renin - Angiotensin - Aldosterone system
creatine
Filtered and neither reabsorbed nor secreted.
electrolytes
Filtered and partly reabsorbed
glucose
Filtered and fully reabsorbed
chemicals
Filtered and fully secreted
TUBULAR SECRETION
Some solutes removed from the blood of the peritubular capillaries back into the filtrate
---Bile acids, ammonia, urea, uric acid and some creatinine are secreted into the filtrate.
----Blood pollutants, morphine, penicillin, aspirin and other drugs are s
TUBULAR REABSORPTION
Most of filtrate removed from the nephron tubules back into the peritubular capillaries blood
65% of reabsorption in the proximal convoluted tubule
Transcellular route
Through the epithelial cells
Paracellular route
Between the epithelial cells
Transport maximum
Is the amount of a substance that can be transported before the transport proteins for that substance become fully saturated
WATER REABSORPTION
Each day, between 150-180 Liters of filtrate
Each day, 1-2 Liters of urine
Each day, about 148-178 Liters reabsorbed
Amounts of H2O reabsorbed
65% in proximal convoluted tubules
15% in descending limbs of Henle
None in ascending limb of Henle
10% in dista
Obligatory water absorption
In PCT and descending LOH
More constant
Facultative water reabsorption
In DCT and CD
Variable, depending on degree of hydration
This reabsorption is controlled by ADH
Steps in Concentration of Urine
As water loss exceeds gain, hypothalamus stimulate secretion of Antidiuretic Hormone (ADH) from the posterior pituitary
2. ADH makes the cells of the DCT and CD more permeable to water
3. More water leaves the DCT and CD and enters concentrated interstiti
Steps in Dilution of Urine
1. As water gain exceeds loss, hypothalamus stops secreting Antidiuretic hormone (ADH)
2 DCT and CD become less permeable to water and less water is reabsorbed
3. Adrenal cortex decreases aldosterone secretion, thus less salt & water is reabsorbed from fi
OBLIGATORY URINE VOLUME
THE MINIMUM URINE VOLUME THAT MUST BE EXCRETED BY THE KIDNEYS TO GET RID OF METABOLIC WASTE AND EXCESS IONS = 0.5 LITERS / DAY.
THE MAXIMUM CONCENTRATION ABILITY OF THE KIDNEYS
= 1200 - 1400 mOsm / Liter
Urine composition
95% H2O
5% solutes (solids)
Electrolytes
Nitrogenous wastes such as urea, creatinine and uric acid
urea from protein metabolism
creatine from muscle metabolism
uric acid nucleic acid metabolism
Characteristics of Urine
Color:- Yellowish to water clear
Turbidity:- Clear without turbidity
Specific gravity:- 1.00 to 1.03
pH:- Acidic, about 6
Abnormal Constituents of Urine
Albuminuria
Glucosuria
Hematuria
Pyuria
Ketonuria
Bilirubinuria
Casts
Renal calculi
THE MICTURITION REFLEX
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