homeostasis Flashcards
what is homeostasis?
the process where internal conditions are maintained within certain limits (a dynamic equilibrium)
what are internal conditions?
includes temperature, pH, sugar and salt conc., water balance ect
what system does homeostasis use?
negative feedback
why do we need to control internal conditions like temperature?
biochemical reactions require specific conditions to work efficiently; cells may be disrupted if solute conc. changes too much
what is the negative feedback mechanism?
a corrective mechanism, where any changes from the norm is detected and the body responds by returning conditions to normal levels
what does negative feedback mechanism involve?
- a detector (receptor) sensing any changes
- a co-ordinator, determines what needs to be done
- an effector, brings about any required changes
what is the output of a negative feedback mechanism?
reduces the original effect of the stimulus
what is the output of positive feedback mechanisms?
enhances the original stimulus
example of positive feedback?
during labour in childbirth, the release of oxytocin intensifies and increases contractions. The increase in contractions releases more oxytocin and the cycle goes on until the baby is born.
what is deamination?
when proteins cannot be stored, so many excess amino acids must be broken down and removed from the body by the liver
where does deamination take place?
in the liver
what is the function of the kidney?
- osmoregulation in the body
- it removes urea from the blood
- controls solutes and pH of the blood
- forms part of the excretory system
what is the kidney made up of?
hundreds and thousands of nephrons
what are nephrons?
they are filtering units of the kidney
what are the distinct parts of the nephrons?
- Bowsman capsule
- proximal and distal convoluted tubules
- loop of Henle
- collecting dust
what brings in the blood to each nephron?
afferent arterioles
what is enclosed in the Bowman’s capsule?
glomerulus (network of blood vessels)
what causes the pressure to build up in the glomerulus?
the efferent arterioles leaving the network are narrower than those entering
what happens to the molecules due to the high pressure of the glomerulus?
the pressure forces molecules out of tiny holes in the capillary walls and lining of the Bowman’s capsule
what do the pedicels do in the Bowmans capsule?
create gaps (fenestrations)
what are podocytes?
covers the glomerular capillary
substances filtered out of blood?
- RBC/WBC
- hormones
- cholestrol
- water ect
Where does selective reabsorption take place?
the proximal convoluted tubule to be reabsorbed by the blood
how is water reabsorbed?
most of it is reabsorbed by osmosis
how is glucose and amino acids reabsorbed?
all of it is reabsorbed by active transport
how are ions reabsorbed?
most are reabsorbed by active transport or facilitated diffusion
describe Na+ and glucose co-transport
Na+ actively pumped out of cell to create conc. gradient. Na+ diffuses into cell by a carrier protein that also binds to glucose. Glucose also brought into the cell then moves out through protein channels into the blood.
How are the cells lining the proximal convoluted tubule specialised for absorption?
- many mitochondria
- many microvilli
- channels at the base of the cells
- cells tightly bound together
- capillaries run close to the cells
why is important that proximal convoluted tubules contain microvilli?
more surface area means more protein carriers, therefore increased uptake of Na+ and glucose
What is the purpose of the Loop of Henle?
concentrates salt in the medulla of the kidney
how is water lost by ultrafiltration reabsorbed?
the collecting ducts in the loop of Henle pass through the salty medulla, allowing water to be reabsorbed
What happens as the filtrate passes up the ascending limb?
Na+ and Cl- is actively pumped out into the medulla
What is a counter-current system?
affects filtrate in the descending limb and water is lost as it passes into the salty medulla
What is the effect of the counter-current system?
the filtrate gets more concentrated as it moves down into the medulla, whilst it becomes more dilute as it passes up the ascending limb
What is the result of the counter-current multiplier?
- a very salty medulla
- as the collecting duct passes through this region, water is lost by diffusion.
- The water diffuses into the vasa recta and is reabsorbed into the blood
What is osmoregulation?
the movement of water from collecting ducts and distal convoluted tubule can be controlled by hormones
What is ADH?
Anti-diuretic hormone
what is the function of ADH?
opens up protein channels in the collecting duct epithelial cells and distal convoluted tubules to be more permeable
What effect does ADH have on the aquaporins?
aquaporins become incorporated in the plasma membranes, from within the cytosol
Where does reabsorbed water from the filtrate go?
the surrounding hypertonic tissue fluid and then passes into blood capillaries
where is ADH secreted?
the posterior pituitary gland (endocrine gland) and its release is controlled via the hypothalamus
What detects the osmotic pressure in the blood?
the osmoreceptor cells in the hypothalamus
what is the role of the hypothalamus for homeostasis?
hypothalamus has osmoreceptor cells which detect the fall in water potential , which results in nerve impulses passing to the posterior pituitary gland which releases ADH into the blood
How are animals adapted with their loop of Henle’s for living in different habitats?
animals in drier climates have longer loops of Henle
What does the length of the loop of Henle signify?
the longer the loop of H, the greater the salt conc. in the medulla. This means more water can be reabsorbed from the collecting duct
what waste products do aquatic animals produce and what issues are associated with this?
they produce ammonia and are highly toxic and requires huge volumes of water to dilute it
