Homeostasis and 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 coordinatior.
Coordinates info 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.
What is osmoregulation important?
- Prevents cells bursting or shrinking when water enters or leaves by osmosis.
- Cellular reactions occur in aqueous solution and so 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.
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.
Define ultrafiltration.
The removal of smaller 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 a 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 glucose selectively reabsorbed into the blood?
- Secondary active transport.
- Uses a co-transport mechanism involving sodium.
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 Henle.
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 Henle?
It creates a low water potential in the medulla, enabling the reabsorption of water.
Describe what happens in the loop of Henle.
- Active transport of sodium and calcium ions 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).
- Hairpin countercurrent 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 or urine controlled?
Controlled by the secretion of antidiuretic hormone (ADH).
Explain the role of the hypothalamus in osmoregulation.
- Osmoreceptors in the hypothalamus detect the concentration of the blood plasma.
- Hypothalamus secretes ADH.e
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 concentration of EPO can lead to anemia.
Outline the potential treatments for kidney failure.
- Low protein diet.
- Control of blood calcium and potassium levels using medication.
- Drug to lower blood pressure.
- Kidney transplant.
What is a transplant?
A medical procedure in which an organ or tissue in an individual in replaced.
