Download - Revision Excretion
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Revision: Excretion
Chapter 7
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Learning Objectives Define excretion and explain the importance
of removing nitrogenous and othercompounds from the body
Outline the function of kidney tubules withreference to ultra-filtration and selectivereabsorption in the production of urine
Outline the role of anti-diuretic hormone
(ADH) in the regulation of osmoticconcentration
Outline the mechanism of dialysis in the caseof kidney failure
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What is excretion?
Excretion - process where metabolic waste
products and toxic materials are removed
from the body of an organism
Egestion - removal of undigested matter from
the alimentary canal. Never been absorbed
into the cells hence not produced as a resultof metabolic changes
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An overview of excretion system
Excretory organs
Kidneys Lungs Skin Liver
Water
Urea
Uric acid
Creatinine
Some salts
Water
CO2
Water
Urea
Uric acid
Creatinine
Some salts
Bile pigments
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Functions of kidney
Main function ofkidneys is to form
urine through
ultrafiltration
Selective
reabsorption of
useful materials
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Functions of the kidneys
Regulates the pH and composition of the
blood plasma.
Regulates the salt and water balance of
the body fluid.
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Ultrafiltration
Blood pressure or hydrostatic
forces out small molecules like
water, salts, glucose and aminoacids and waste materials
include excess mineral salts,
nitrogenous wastes (urea,
creatinine, uric acid). All thesemake up the filtrate.
Selective reabsorption
Most water reabsorbed by
osmosis. Some mineral salts,all glucose and all amino acids
are actively reabsorbed through
the nephron
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The mammalian
urinary system
Structure
Urinary system
Longitudinal section of kidney
Structure of nephron
Function
Formation of urine (ultrafiltration and selective
reabsorption
Kidneys as osmoregulators
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Urinary system
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Theu
rinary system The urinary system comprises of:
- 2 kidneys
- 2 ureters
- 1 urinary bladder
- 1 urethra
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Longitudinal section of kidney
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Stru
ctu
re of a neph
ron Each nephron comprises of:
Bowmans capsule and glomerulus
Proximal and distal convoluted tubules
Loop ofHenl
Collecting duct
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Structure
of th
enephron
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Formation of urine
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Kidneys as osmoregu
lators Water potential of the blood has to be kept
relatively constant.
Control of water content of the body is
known as osmoregulation.
The kidney, together with thehypothalamus and pituitary gland, are
responsible for osmoregulation in humans.
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Kidneys as osmoregu
lators The hypothalamus continuously monitors
the concentration of the blood.
The pituitary gland secretes the hormone
called vasopressin oranti-diuretic
hormone (ADH).
Anti-diuretic hormone (ADH) increases
water re-absorption by the kidney tubules.
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Kidneys as
osmoregu
lators
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Dialysis
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Dialysismembrane
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Kidney failu
re1. In dialysis, blood is drawn from an artery
in the patients arm and allowed to flow
through the tubing in a dialysis machine.
2. The dialysis machine contains fluid
consisting of water and other substances
such as salt.
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Kidney failu
re3. As the patients blood passes through the
dialysis machine, it is separated from the
fluid by a partially permeable membrane.
4. Small molecules such as urea diffused
through the membrane into the fluid.
5. Big molecules, such as proteins and
blood cells, remains in the tubing.
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Kidney failure The filtered blood is then returned to a
vein in the patients arm.
Dialysis can be inconvenient and
expensive for the patients.
A better long-term solution for kidneyfailure is a kidney transplant. However,
there are drawbacks as well.
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Conclusions Excretion is process where metabolic waste
products and toxic materials are removed from thebody of an organism (different from egestion)
Kidneys produce urine through ultrafiltration and
selective reabsorption
Kidneys are involved in osmoregulation,regulation of pH in blood and regulation of bloodplasma composition.
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Each nephron consists of a renal (Bowmans)
capsule, the glomerulus, first (proximal)
convoluted tubule, loop ofHenl and second(distal) convoluted tubule).
Urine is formed by ultrafiltration and selective
reabsorption.
The hormone ADH regulates the amount of
water reabsorbed by the kidney tubules.