Osmoregulation, the kidneys and DNA control Flashcards
Describe the blood vessels associated with a nephron.
Wide afferent arteriole from renal artery enters renal capsule and forms glomerulus (branched knot of capillaries which combine to form narrow efferent arteriole).
Efferent arteriole branches to form capillary network that surrounds tubules.
Describe the gross structure of a mammalian kidney.
Fibrous capsule protects kidney. Cortex: outer region, made of Bowmans capsules, convoluted tubules and blood vessels.
Medulla: Inner region, consists of collecting ducts, loops of Henle and blood vessels.
Describe the sections of a nephron.
-Bowman’s capsule at start of nephron: cup-shaped, surrounds glomerulus, inner layer of podocytes.
-Proximal convoluted tubule: series of loops surrounded by capillaries, walls of epithelial cells with microvilli.
-Loop of Henle
-Distal convoluted tubule: similar to PCT but fewer capillaries.
-Collecting duct: DCT from several nephrons empty into collecting duct, which leads into pelvis of kidney.
What is deamination?
The removal of the amino group in an amino acid
What is urea?
A waste molecule produced in the liver as a product of amino acid breakdown which is excreted in urine.
Describe the process of ultrafiltration
Occurs in Bowman’s capsule. High hydrostatic pressure in glomerulus forces small molecules out of capillary fenestrations against osmotic gradient.
Basement membrane acts as filter. Blood cells and large molecules remain in capillary.
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
State what happens during selective reabsorbtion and where it occurs.
Useful molecules from glomerular filtrate like glucose are reabsorbed into the blood. Occurs in the proximal convoluted tubule.
How does the kidney produce urine?
After selective reabsorption, filtrate passes through Loop of Henle, which acts as countercurrent multiplier and then through distal convoluted tubule, where water and mineral ions are reabsorbed. More water is reabsorbed in collecting duct. Remaining fluid (urine) contains only waste materials and water.
What happens in the loop of Henle?
- Active transport of Sodium and chloride out of ascending limb
- Water potential of interstitial fluid decreases
- Osmosis of water out of descending lim (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.
What is the pituitary gland?
An endocrine gland found in the brain which secretes regulatory hormones into the bloodstream. These hormones have their own effects or stimulate other glands to secrete hormones. The pituitary gland is important in osmoregulation because it secretes ADH.
What is antidiuretic hormone?
A hormone secreted by the posterior pituitary gland which decreases water loss in urine by increasing the water reuptake capacity of the collecting duct.
What are aquaporins?
A type of intrinsic membrane protein channel which allows water to pass across membranes.
How does ADH increase water reuptake in the collecting duct?
ADH is secreted by the posterior pituitary gland and it binds to receptors on the collecting duct cells. This triggers an intracellular signaling cascade which results in exocytosis of vesicles containing aquaporins. These aquaporins become part of the plasma membrane after exocytosis
Describe the process of ADH secretion by the pituitary gland
-Osmoreceptors in the hypothalamus detect low blood water content and generate an action potential. This potential travels down the pituitary stalk to the pituitary gland. The pituitary gland secretes ADH into the bloodstream.
What are transcription factors?
Proteins which bind to regulatory regions of DNA and control DNA transcription. They can turn genes on and off.
How can peptide hormones affect DNA transcription?
By binding to extracellular receptors which produce changes within cells. The changes are Brough about by intracellular signaling cascades.
Why must peptide hormones bind to extracellular receptors?
Peptide hormones are hydrophilic and can’t pass through the plasma membrane.
How can steroid hormones affect DNA transcription?
They can diffuse into the nucleus and bind to nuclear or cytoplasmic receptors which can directly alter DNA transcription by binding to regulatory sections.
Give one example of a peptide hormone
Insulin. It’s secreted by beta cells of the pancreas and it regulates blood glucose concentration.
Give one example of a steroid hormone.
Testosterone. It binds to the androgen receptor which acts as a transcription factor. It’s secreted by the testes.
How do transcription factors work?
They bind to DNA and either promote or inhibit transcription by blocking or enhancing the activity RNA polymerase.
