2.4 Digestion and excretion
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- Created by: amibhi
- Created on: 04-05-24 23:24
Define the term excretion
- Excretion= the removal of metabolic wastes from the body
- // process that rids the body of nitrogenous metabolites
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Explain the importance of removing metabolic waste
- Nitrogenous wastes must be removed because the amino group is highly toxic
- however, a.a. and proteins are high in energy so it would be wasteful to excrete them
- Ammonia
- animals excreting ammonia needs access to lots of water
- released across whole body surface
- Urea
- no access to sufficient water to excrete ammonia
- produced in liver, product of ornithine cycle
- low toxicity, can be transported in circulatory system
- energetically expensive
- Uric acid
- birds, insects, reptiles
- relatively non-toxic, not readily dissolvable in water
- even more energetically expensive
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Describe the histology and structure of the liver
- only organ capable of natural regeneration
- performs many metabolic and homeostatic functions
- endocrine function
- iron and copper storage
- detoxification
- hepatic arteries supply liver with oxygenated blood from heart -> provides plenty of energy for respiration (25%)
- hepatic veins takes deoxygenated blood away from liver - which rejoins the vena cava (75%)
- bile duct -> where bile is secreted, carried to the gall bladder where it is stored until required by small intestines
- hepatic portal vein brings blood from small intestine, blood is rich in products of digestion
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Describe the formation of urea in the liver
- A.A. catabolism
- breakdown of a.a. occur by transamination and deamination
- products will be detoxified by urea cycle
- breakdown of a.a. occur by transamination and deamination
- transamination:
- Amino acid + a-Ketogluterate -> a-keto acid + glutamate
- can be: acetoacetyl coA, acetyl coA, pyruvate
- Amino acid + a-Ketogluterate -> a-keto acid + glutamate
- deamination
- Glutamate + water -> a-Ketoglucerate + ammonia
- Ornithine cycle
- ammonia released by deamination is removed by liver and converted to urea
- all urea is synthesised by liver and excreted by kidneys
- some diffuses into intestine - converted into ammonia by enteric bacteria
- CO2 and ammonia enter and gets converted into carbarnoyl phosphate
- uses 2 ATP molecules (broken down)
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Describe the roles of the liver in detoxification
- xenobiotics are substances that aren't normally present in body
- liver is responsible for neutralising xenobiotics - through biotransformation (modifying chemical constitution)
- detoxification of drugs:
- phase 1 -> oxidation, reduction e.t.c.
- phase 2 -> conjugation
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Describe the histology and structure of the kidney
- consists of numerous tubules
- functions in both osmoregulation and excretion
- supplied with blood from renal artery and is drained by renal vein
- surrounded by a tough capsule, outer region is the cortex and inner is medulla
- central region is the pelvis, which leads into ureter
- renal cortex have cortical nephrons (85%) and juxtamedullary nephrons (15%)
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Describe the structure of a nephron and its associ
- functional unit of the vertebrate kidney
- made up of:
- glomerulus
- Bowman's capsule
- proximal tubule
- loop of Henle
- distal convulted tubule
- collecting duct
1. fluid from blood is pushed into BC by ultrafiltration
2. fluid leaves BC and flows to the proximal tubule where composition of fluid is altered by selective reabsorption
3. goes into loop of Henle, which is a hairpin counter-current multiplier
4. substances are reabsorbed back into tissue fluid and capillaries surrounding nephron tubule
5. fluid passes into distal convoluted tubule and then collecting duct as urine
- Bowman's capsule
- porous capillaries and specialized cells are permeable to water and small solutes, but not larger molecules
- high hydrostatic pressure forces small molecules from blood across BC into renal tubules
- Adaptations of glomerulus (ultrafiltration)
- afferent arterioles have a larger diameter than efferet arterioles -> causes increase in blood pressure
- gaps between epithelial cells allow molecules to leave blood
- basement membrane acts as a filter allowing small molecules to pass
- resulting filtrate contains water, salts, glucose, a.a., vitamins e.t.c
- Proximal convoluted tubule (selective reabsorption)
- reabsorption of: glucose, a.a.
- toxic materials are actively secreted into filtrate (ammonia, organic acids)
- maintains pH balance
- has microvilli -> increase SA
- co-transporter proteins
- many mitochondria
- Na/K pumps
- Loop of Henle
- filtrate enters descending limb ->
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Describe / explain the production of urine
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Explain the control of water content of the blood
- volume and osmolarity of urine is adjusted according to water and salt balance of animal and rate of urea production
- low salt -> high fluid intake -> hypoosmotic urine
- high salt -> low fluid intake -> hyperosmotic urine
- ADH
- produced by hypothalamus and is stored in pituitary gland
- osmoreceptor cells monitors osmolarity of blood and release ADH
- ADH influences water uptake by increasing the number of aquaporins in membranes of collecting duct
- -> less concentrated urine
1. Sweating causes blood osmolarity to increase
2. Osmoreceptors sense change and hypothalamus releases ADH
3. ADH transported to collecting duct cells, increasing number of aquaporins to make membrane more permeable to water
4. more water gets reabsorbed into blood by omsosis
5. less urine, with a lower water potential is released
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