Homeostasis & The Kidney Flashcards
What is homeostasis?
The maintenance of a state of dynamic equilibrium in the body despite
fluctuations in internal and external conditions.
Why is homeostasis important?
To ensure optimum conditions for enzymes and cellular processes in the body.
Define negative feedback.
Self-regulatory mechanisms return the internal environment to the optimum when there is a fluctuation.
Define positive feedback.
A fluctuation which triggers changes that result in an even greater deviation from the normal level.
What is the set point?
A desired value or range of values determined by a coordinator.
Describe receptors and effectors
- Receptors - specialised cells located in sense organs that detect a specific stimulus
Effectors - muscles or glands which enable a physical response to a stimulus
Describe the role of the coordinator.
Coordinates information from the
receptors and sends instructions to the effectors.
State the components of a negative feedback system.
- Set point
Receptors Coordinator - Effectors
What is the mammalian kidney?
One of a pair of organs in the abdomen that has a role in osmoregulation and nitrogenous excretion.
What is osmoregulation?
The regulation of the water potential of body fluids (e.g. blood, tissue fluid, lymph) by the kidney.
Why is osmoregulation important?
- Prevents cells bursting or shrinking when water enters or leaves by osmosis
Cellular reactions occur in aqueous solution ..
water levels affect concentrations and the rate of reactions in cells
Define excretion.
The process of removing metabolic
waste from an organism.
Describe how excess amino acids are
excreted.
Amino acids deaminated in the liver (removal of
amino group) to form ammonia
* Ammonia converted to urea (less toxic)
* Urea transported into the blood plasma and eliminated by the kidneys
What is the function of the renal artery?
Supplies blood to the kidneys.
What is the function of the renal vein?
Drains blood from the kidneys.
What is the function of the ureter?
Takes urine to the bladder from the
kidneys.
What is the function of the urethra?
Releases urine from the bladder, out of the body.
Describe the gross structure of a mammalian kidney.
Fibrous capsule - protects kidney
Cortex - outer region consists of Bowman’s capsules, convoluted tubules, blood vessels
Renal pyramids - cone-shaped subdivisions
Renal pelvis - funnel-shaped dilated section of
ureter
Medulla - inner region consists of collecting ducts, loops of Henle, blood vessels
What is a nephron?
The functional unit of the mammalian
kidney.
Where are nephrons found within the
kidneys?
Part of the nephron is
located in the medulla and part in the cortex.
Describe the blood vessels associated with a nephron.
Wide afferent arteriole from renal artery enters renal capsule and forms the glomerulus, a branched knot of capillaries which combine to form narrow efferent arteriole.
Efferent arteriole branches to form capillary network that surrounds tubules.
Define ultrafiltration.
The removal of small molecules, water and ions from the blood in the glomerulus of the kidney at high pressure.
Describe the process of ultrafiltration.
Occurs in Bowman’s capsule
High hydrostatic pressure in glomerulus forces small molecules (e.g. urea, water, glucose, ions) out of capillary fenestrations against osmotic gradient
Basement membrane acts as filter. Blood cells and large molecules (e.g. proteins) remain in capillary
Why is there a build-up of pressure in the glomerulus?
Afferent arteriole leading into the glomerulus is wider than the efferent arteriole taking blood from the glomerulus.
How are cells of the Bowman’s capsule adapted for ultrafiltration?
- Fenestrations between epithelial cells of capillaries
Fluid can pass between and under folded membrane of podocytes
What happens during selective reabsorption?
- Useful molecules from glomerular filtrate (glucose, some water, some ions) are reabsorbed into the blood
- Involves membrane transport proteins
Where does selective reabsorption
occur?
Proximal convoluted tubule
How are cells in the proximal convoluted tubule adapted for selective reabsorption?
Microvilli provide a large surface area for co-transporter proteins
* Many mitochondria produce ATP for active transport of glucose into intercellular
spaces
+ Folded basal membrane provides a large surface area
* Tight junctions stop reabsorbed materials leaking back into the filtrate
*
Peritubular capillaries extend into the medulla enabling reabsorption of materials
By what mechanism are amino acids and filtered glucose selectively reabsorbed into the blood?
Secondary active transport
* Uses a co-transport mechanism involving Na+
By what mechanism are mineral ions selectively reabsorbed into the blood?
Active transport
By what mechanism is water selectively reabsorbed into the blood?
Osmosis
How are filtered proteins (and some urea) selectively reabsorbed into the
blood?
Via Diffusion
Describe the loop of Henlé.
A loop consisting of a descending limb (dips into the medulla) and ascending limb (rises into the cortex) surrounded by blood capillaries.
What is the function of the loop of Henlé?
It creates a low water potential in the medulla, enabling the reabsorption of water.
Describe what happens in the loop of
Henlé.
Active transport of Na and Cl out of ascending limb
Water potential of interstitial fluid decreases
Movement of water out of descending limb via osmosis (ascending limb is impermeable to water)
Water potential of filtrate decreases going down descending limb - lowest in medullary region, highest at top of ascending limb
Hair-pin counter-current multiplier
What is an endocrine gland?
A gland of the endocrine system that secrete hormones directly into the bloodstream.
How is the concentration and volume of urine controlled?
Controlled by the secretion of anti-diuretic hormone (ADH).
Explain the role of the hypothalamus in osmoregulation.
- Osmoreceptors in hypothalamus detect the concentration of the blood plasma
- Hypothalamus secretes ADH
Explain the role of the posterior pituitary gland in osmoregulation.
Stores and secretes the ADH produced by the hypothalamus.
Describe how ADH affects the reabsorption of water from the kidney
tubules.
ADH causes insertion of aquaporins into the plasma membranes of cells of the DCT and collecting duct
Increases permeability of the DCT and collecting duct
More water reabsorbed More concentrated urine produced
Describe the effects of kidney failure.
- Build-up of toxic waste products (e.g. urea) causes symptoms such as vomiting
Fluid accumulation leads to swelling - Disruption to electrolyte balance can make bones more brittle
- High concentrations of renin may lead to hypertension
Low concentrations of EPO can lead to anaemia
Outline the potential treatments for
kidney failure.
Low protein diet
* Control of blood calcium and potassium levels using medication
* Drugs to lower blood pressure
* Renal dialysis
Kidney transplant
Describe renal dialysis.
- Medical procedure that artificially filters the blood
- Relies on a partially permeable membrane between the patient’s blood and dialysis fluid
- Two types: haemodialysis and peritoneal dialysis.
What is a transplant?
A medical procedure in which an organ or tissue in an individual is replaced.
Describe how animal excretory products
can differ.
Freshwater animal species excrete ammonia
* Reptiles, birds and insects produce uric acid
* Mammals excrete urea
How does the length of the loop of Henlé differ between mammals?
Length of the loop varies depending on the availability of water in the mammal’s environment
* Longer loop in desert animals (e.g. kangaroo rat) to allow greater time for reabsorption of water and salts
