Homeostasis And The Kidney💦 Flashcards
What is homeostasis?
The maintenance of a constant internal environment within a living organism
What is negative feedback?
Where a stimulus causes an opposite output/brings about corrective mechanism in order to maintain an ideal level/restore norm
What must each control system have?
- A receptor - detects a stimulus - a change from the norm
- A coordinator - receives and controls information from receptor and triggers an action
- An effector - carries out action (corrective mechanism)
What is osmoregulation?
- Carried out by kidneys
- Maintenance of set water potential of blood/homeostatic control of body water
- Involved in excretion
What is excretion?
- Removal of waste products produced during cellular metabolisms
- Forms urine
What are the main organs in the urinary system?
The kidneys
What is the role of the kidneys?
- To filter waste products out of the blood
* To regulate the water potential of the blood
Where does each kidney relieve it’s blood supply from?
The renal artery - a branch of the aorta
How does the filtered blood leave the kidneys?
Along the renal veins
Where does the urine travel?
- Passes down a muscular tube called the ureter
* There is a ureter connecting each kidney to the bladder - a muscular sac that stores urine
What happens during urination?
- Sphincter muscle relaxes
* Urine passes out of the body, along the urethra
What is the structure of the surrounding layer? (Kidney structure)
- Layer of adipose (fat) tissue and a layer of fibrous connective tissue
- These keep kidneys in position and protect them from mechanical damage
What is the structure of the cortex? (Kidney structure)
- The dark outer region
- Filtration is carried out by the nephrons here
- Dense capillary network - receives blood from renal artery
What is the structure of the medulla? (Kidney structure)
- The lighter inner region
* Each nephron extends across the medulla to form structures called renal pyramids
What is the structure of the pelvis? (Kidney structure)
- The renal pyramids projects into the pelvis
* Urine passes out into the pelvis before it passes down the ureter
Describe the nephron blood supply
- Renal artery branches to form arterioles
- Each Bowman’s capsule is supplied with blood by an afferent arteriole
- Afferent arteriole branches inside the Bowman’s capsule to form the glomerulus
- Capillaries in glomerulus join up to form efferent arteriole, which takes blood away from the Bowman’s Capsule
What is the effect of the afferent arteriole being wider than the efferent?
•More blood is carried to the glomerulus than carried away
Describe the endothelium of the capillary (Microstructure)
- First cell layer
* In the glomerulus, this single layer of cells has thousands of gaps (fenestrations)
Describe the basement membrane (Microstructure)
•Between two cell layers
•Composed of glycoprotein and collagen fibres
•Mesh-like structure acts as a filter
- water and small solutes are forced out of the blood
-blood cells and large solutes are prevented from leaving
Describe the podocytes (Microstructure)
- The second cell layer - epithelial cells
- Have foot-like processes that wrap around the capillaries
- Gaps between them
What is deamination?
The break down of excess amino acids in the liver for:
•Building new proteins
•Produce waste (urea) - amino group combines with carbon dioxide to form urea
What is ultrafiltration?
•The filtering (under pressure) of small molecules out of the blood and into the Bowman’s capsule
Describe the process of ultrafiltration
- Gaps in capillary endothelium and Bowman’s capsule wall allow most molecules to pass through
- Basement membrane prevents large molecules from passing through
- Blood pressure in kidney is higher than in the other organs - pressure maintained by glomerulus (wide afferent arteriole)
- More blood goes into the glomerulus than leaves
- Hydrostatic pressure builds up, forcing substances through the endothelial pores, across the B.membrane and into the B.capsule
What is the composition of glucose filtrate in comparison to plasma? (Reabsorption)
- Water - both 900gdm-3
- Protein - plasma 80gdm-3
- Glucose - both 1gdm-3
- Amino acids - both 0.5gdm-3
- Urea - both 0.3gdm-3
- Inorganic ions - both 7.2gdm-3
What is selective reabsorption? (Reabsorption)
All glucose, amino acids, vitamins and many Na+ Cl- are actively transported out of the proximal convoluted tubule and back into the blood
Describe the reabsorption of water (Reabsorption)
- Uptake of substances means blood in capillaries surrounding the nephron have a low water potential
- Large amounts of water passes out of the filtrate in the proximal convoluted tubule and back into the blood by osmosis
What are the adaptations of the proximal convoluted tubule? (Reabsorption)
- Microvilli - large S.A for absorption
- Numerous mitochondria provide ATP for active transport
- Close to capillaries - short diffusion pathway
- Circulation of blood maintains a concentration gradient
What is the function of the loop of Henle?
To create an area of high solute concentration deep in the medulla
- Generates a water potential gradient between the filtrate and the tissue fluid of the medulla
- This allows the concentration/volume of urine to be adjusted when necessary (osmoregulation)
Describe the role of the loop of Henle as a counter current multiplier
- Ascending limb more permeable to salts than water
- As filtrate moves up, Na and Cl ions move out (passively first and the actively pumped) into surrounding tissue
- Causes water to pass out of descending limb via osmosis
- Filtrate becomes more concentrated as it passes down the descending limb
- Net result - solute concentration at any part of loop is lower in the ascending limb than it is in the descending limb
How does the role of the loop impact on the function of the collecting duct?
- As the collecting ducts pass through the medulla to the pelvis they pass through the region of high solute concentration
- Water is drawn out of the collecting ducts by osmosis
- Creates more concentrated urine
How is osmoregulation carried out? (Collecting duct)
- Osmoreceptors In hypothalamus of brain react to changes in solute concentration of blood as it flows through the hypothalamus
- Stimulates posterior pituitary gland to secrete more/lessADH
- ADH makes walls of collecting duct and distal convoluted tubule more/less permeable through aquaporins
- More water reabsorbed
- Restores normal water potential of blood and produces small/large volume of hyper/hypotonic urine
What does ADH stand for and what does it do?
- Antidiuretic hormone
* Makes walls of CD and DCT permeable
What is dialysis fluid?
- Has same composition as that desired in the blood plasma
- Wastes, toxic molecules and excess fluid diffuse from blood into dialysis fluid
- Counter current flow of blood and dialysis fluid ensures a constant diffusion gradient is maintained
How does haemodialysis work?
- Blood passes through an artificial kidney machine (at hospital or home)
- A shunt is used to access the bloodstream (tube that connects an artery to a vein)
- Blood flows from this tube into the machine and back to the patient
- Inside machine, blood flows over the surface of the partially permeable dialysis membrane
- Wastes diffuse into dialysis fluid
- Purified blood is returned to the patient
Positives and negatives of haemodialysis
POSITIVES •Patient can drink and eat what they want (to an extent) NEGATIVES •Restrictive •Session lasts 2-6 hours •2-3 sessions a week
How does peritoneal dialysis work?
- Insert dialysis fluid into peritoneal cavity using a catheter
- Waste products and excess water pass through the peritoneal membrane into this cavity
- After several hours, fluid is drained out and discarded
Positives of peritoneal dialysis
- During period of drainage of fluid, patient can carry on with normal activities
- Usually carried out at home
What are some causes of kidney failure?
- Diabetes
- High-blood pressure
- Auto-immune disease
- Infection
- Injury
What are some treatments of kidney failure?
- Low-protein diets
- Medication to reduce blood pressure
- Medication to control K+ and Ca- levels
What are the pros of kidney transplant? (over dialysis)
- Most straightforward transplant
- Reasonable chance of success(80%)
- Less expensive in long term
What are the cons of kidney transplant? (Over dialysis)
- Similar tissue and blood type
- Rejection means returning to dialysis
- Have to take immunosuppressants for rest of life
- Long waiting list(4000)
- More expensive in short term
Describe nitrogenous waste in fish
- Release nitrogen as ammonia
- This is extremely soluble
- Quickly diffuses out of gills and dilutes
Describe nitrogenous waste in reptiles, birds and insects
•Excrete nitrogen and uric acid which requires energy
•This is almost insoluble in water and is non-toxic
•Very little water is needed to excrete uric acid
- conserve body water and live in arid environments
Describe nitrogenous waste in mammals
- Excrete as urea
- Requires less water than ammonia
- Energetically expensive, but prevents dehydration
How does the length of the loop of Henle link to the environment?
- In hot conditions, there will be a longer loop
- The thicker the medulla, the longer the loop
- The longer the loop, the greater the solute concentration set up in the medulla - more water is reabsorbed - more concentrated urine
Explain how ADH works
- ADH binds to receptors in membrane of CD epithelial cells
- Stimulates formation of vesicles containing aquaporins
- These move to inner membrane of CD epithelial cells and fuse with it, inserting aquaporins into membrane
- Water can now move along a water potential gradient, through the epithelial cells and into medulla tissue fluid, and then into capillaries - raises water potential of blood
Approximately what percentage of the plasma leaves the blood and enters the glomerula filtrate?
20%
What percentage of urea is reabsorbed and why?
50%
-Because a concentration gradient exists
What percentage of water is reabsorbed?
85%
What is the function of the ascending limb?
To create a water potential gradient between the filtrate and the tissue fluid of the medulla
Why is the hydrostatic pressure of the blood in the glomerulus very high?
- Contraction of the left ventricle (renal artery branches from the aorta)
- Efferent arteriole leaving the glomerulus is narrower - creating a bottleneck effect
What is the descending limb highly permeable to? (Loop of Henle)
Water
What is the ascending limb highly permeable to? (Loop of Henle)
Ions
What are the walls of the blood capillaries surrounding the loop permeable to? (Loop of Henle)
Freely permeable to both water and ions
As the filtrate moves down the descending limb it…
Loses water - lower water potential
As the filtrate moves up the ascending limb it…
Loses ions - higher water potential
At the apex of the loop…
The filtrate reaches a maximum ion concentration
As the filtrate enters the DCT…
It has a higher water potential than the tissues of the medulla
As the filtrate moves down the collecting duct…
- It meets tissue fluid with a lower water potential
- So water moves out of filtrate via osmosis along entire length of CD
- Produces urine that is reduced in volume and has a lower water potential than blood
