Homeostasis Flashcards
Define homeostasis
The maintenance of a stable equilibrium in the conditions inside the body
What do negative feedback loops aim to do?
Reverse the initial stimulus
What do positive feedbacks aim to do?
A change in the internal environment is detected by sensory receptors and effectors are stimulated to reinforce the change and increase the response
Define thermoregulation
Maintenance of a relatively constant core body temperature to maintain optimum enzyme activity
Define ectotherm
Animals that use their surroundings to warm their bodies so their core temperature is heavily dependent on outside environment
Define endotherm
Animals that rely on their metabolic processes to warm their bodies and maintain their core temperature
Draw a graph to show the effect of changes in the internal and external temperature on ectotherms and endotherms
External temperature on x axis
Body temperature on y axis
Ectotherm linear relationship not passing through the origin
Endotherm horizontal line around 37C
What are behavioural responses that some ectotherms have to changes in temperature?
Orientating themselves to have maximum exposure to the sunshine
Conduction by placing their bodies on the warm ground
Seeking shade to decrease temperature
What are 2 key physiological responses ectotherms have?
Colour changes in their skin
Alter heart rate to change metabolic rate
Where are peripheral temperature receptors in endotherms?
Skin
Where are the 2 temperature receptors found in the body?
Skin
Hypothalamus
What are the three mechanisms that endotherms have to cool down?
Vasodilation
Increased sweating
Reducing the insulating effect of hairs
Explain what vasodilation is and how it leads to cooling of the body
Arteries near the surface of the skin dilate
Forces blood through capillary networks near the surface of the skin
Skin flushes and cools as a result of increased radiation
Explain how sweating leads to heat loss
Sweat evaporates from the surface of the skin so heat is lost and the surface below cools
Explain how hair can be used to cool the body
The erector pilli muscles in the skin relax
Hairs lie flat on the skin
Avoids trapping an insulating layer of air
Describe the 4 processes that occur to warm up an endotherm
Vasoconstriction
Decreased sweating
Raising the body hair or feathers
Shivering
Explain how vasoconstriction causes warming in the body
Arterioles near surface of the skin constrict
Arteriovenous shunt vessels dilate so little blood flows through the capillary networks close to the surface of the skin
Little radiation occurs and warm blood is kept well below the surface
Explain the process of shivering within an endotherm
The rapid, involuntary contraction and relaxation of large voluntary muscles in the body
What are the two control centres in the control of thermoregulation?
Heat loss centre
Heat gain centre
Explain how the heat loss centre is activated
Temperature of the blood flowing through the hypothalamus increases
Sends impulses through the autonomic motor neurons to effectors in the skin and muscles triggering responses to lower core temperature
Explain how the heat gain centre is activated
Temperature of the blood flowing through the hypothalamus decreases
Sends impulses through the autonomic nervous system to effectors in the skin and muscles triggering responses to increase core temperature
How is oxygenated blood supplied to the liver?
Hepatic artery
How is deoxygenated blood removed from the liver?
Hepatic vein
What is the role of the hepatic portal vein?
To carry blood containing the products of digestion straight from the intestines to the liver
What are liver cells called?
Hepatocytes
What are the key features of hepatocytes?
Large nuclei
Prominent golgi apparatus
Lots of mitochondria
Where does the blood from the hepatic artery and portal vein mix?
In the sinusoid which is surrounded by hepatocytes
What type of cell does the sinusoid contain?
Kupffer cells
What is the role of a Kupffer cell?
Macrophage of the liver ingesting foreign particles and helping to protect against disease
Hepatocytes secrete bile. Where does it go?
Into the canaliculi
Canaliculi then drains the bile into bile ducts which take it to the gall bladder
What are the three major roles of the liver?
Carbohydrate metabolism
Deamination of excess amino acids
Detoxification
How do hepatocytes aid carbohydrate metabolism?
When blood glucose levels rise the insulin levels rise and stimulate hepatocytes to convert glucose to glucagon
When blood glucose levels fall the glucagon levels rise and this stimulates hepatocytes to convert glycogen into glucose
What is transamination?
The conversion of one amino acid into another
Why is transamination important?
Diet doesn’t always contain the required balance of amino acids so this helps overcome this issue
What is deamination?
The removal of an amine group from a molecule
Explain what happens to excess amino acids that are absorbed by the liver
Amino acid molecules are split
The amino group combines with carbon dioxide to form urea
Urea is excreted via the kidneys
Rest of amino acid molecule is used in respiration
What does the ornithine cycle show?
The enzyme controlled set of reactions that convert ammonia into urea
Explain how the liver breaks down hydrogen peroxide
Hepatocytes contain catalase which splits hydrogen peroxide into oxygen and water
Explain how the liver breaks down alcohol
Ethanol is the active agent in alcohol
Hepatocytes contain alcoholic dehydrogenase
Ethanol broken down into ethanal
Ethan is then converted into ethanoate which can be used to build up fatty acids or it is used in cellular respiration`
What are the kidneys normally surrounded by?
A thick protective layer of fat and a layer of fibrous connective tissue
What are the two crucial homeostatic functions of the kidney?
Excretion
Osmoregulation
How does oxygenated blood arrive at the kidney?
Renal arteries coming from the abdominal aorta
How does deoxygenated blood leave the kidney?
Renal vein into the inferior vena cava
What liquid is produced by the kidneys?
Urine
What tube does urine enter having left the kidney?
Ureter
What are the three main areas of the kidney?
Medulla
Cortex
Pelvis
Describe the structure and function of the kidney cortex
Dark outer layer
Dense capillary network carrying blood from renal artery to the nephrons
Filtering of blood occurs here
Describe the structure and function of the kidney medulla
Lighter colour
Contains tubules of nephrons that form pyramids of the kidney and collecting ducts
Describe the structure and function of the pelvis
Central chamber of the kidney where urine collects before passing out of the ureter
Describe the structure of the Bowman’s capsule
Cup shaped structure that contains the glomerulus
Describe the structure and function of the glomerulus
Tangle of capillaries
More blood enters the capillaries than leaves as ultrafiltration occurs
Describe the structure and function of the proximal convoluted tube
First coiled region of tubule after the Bowman’s capsule
In the cortex of the kidney
Many substances needed by the body are reabsorbed into the blood
Describe the structure and function of the Loop of Henle
A long tubule that creates a region with a very high solute concentration in the tissue fluid in the medulla
Describe the structure and function of the distal convoluted tubule
Second twisted tubule where fine tuning of the water balance occurs
Permeability of the walls varies with levels of ADH in the blood
Ion and pH regulation occurs here too
Where is ADH produced and secreted?
Produced in the hypothalamus
Secreted into the posterior pituitary gland
How does ADH work?
Increases the permeability for the distal convoluted tubule and collecting duct to water
