Week 8 - Renal system Flashcards
Renal system- functions
Filter blood: remove METABOLIC WASTE
Regulate:
- Fluid and electrolyte balance my regulating OSMOLARITY → adjusts blood vol & pressure
- ERYTHROPOIESIS by releasing Erythropoeitin
- Plasma conc (Na+, K+, Cl-)
- Acid-base balance + blood pH
- Vital to many metabolic functions: DETOXIFYING substances in the blood, ACTIVATING VitD, making new glucose
Nitrogenous wastes
UREA:
- Proteins → amino acid → NH2 removed →NH2 forms ammonia (which is toxic), liver converts to urea
CREATINE:
- Creatine phosphate catabolism in skeletal muscle
URIC ACID:
- Nucleic acid catabolism (from recycling of RNA)
Excretion
- RESPIRATORY: CO2
- INTEGUMENTARY: water, inorganic salt, lactic acid, urea (via sweat)
- DIGESTIVE: water, salts, CO2, lipids, bile pigments, cholesterol
- URINARY: metabolic waste, toxins, drugs, hormones, salts, H+ & water
Kidneys - anatomy
Connective tissue covering:
- PARIETAL PERITONEUM: covers anterior aspect
- RENAL FASCIA: binds kidneys to abdominal wall
- PERI-RENAL FAT CAPSULE: cushions kidney
- FIBROUS CAPSULE: layer of collagen fibres; encloses kidney like cellophane wrapper, protects from trauma & infections
Blood vessels, nerves & ureter enter HILUM
Kidneys - internal anatomy
- RENAL CORTEX: superficial layer
- RENAL MEDULLA: inner portion consisting of RENAL PYRAMIDS separated by RENAL COLUMNS. Tip of pyramid: RENAL PAPILLA opens into MINOR CALYX
- RENAL SINUS: cavity- houses initial segment of urine drainage system, cuplike structure
- Minor calyces drain urine into the MAJOY CALYCES, empty into RENAL PELVIS, empty to URETER
- KIDNEY LOVE: pyramid & overlying cortex
Nephrons
CORTICAL NEPHRONS (85%)
- close to kidney surface
- short nephron loops, only small proportion in medulla
JUXTAMEDLLARY NEPHRONS (15%)
- very long nephron loops, extend deep into renal medulla
- maintain salt gradient, helps conserve water by concentrating urinw
Renal tubule - anatomy
PROXIMAL CONVOLUTED TUBULE (PCT)
- longest, more coiled, simple cuboidal w/ microvilli
NEPHRON LOOP (LOOP OF HENLE)
- descending & ascending limbs
- thick segment (simple cuboidal) initial part of descending limb & part or all of ascending. active transport- salt
- thin segment (simple squamous) → very water permeable
DISTAL CONVOLUTED TUBULE (DCT)
- nephron loop returns to cortex, shorter, less convoluted
- cuboidal, smooth surface w/ minimal microvilli
Blood supply - kidneys
Renal artery divides into segmental arteries that give rise to:
- interlobar arteries : up renal column betw. pyramids
- arcuate arteries - over pyramids
- interlobar (or radiate) arteries → up to cortex
- branch into afferent arterioles → each suppying one nephron
Neural regulation - kidneys
- renal nerves enter the hilum
- follow branches of renal arterioles and innervate the afferent & efferent arterioles
- kidneys receive SYMPATHETIC info from renal plexus w/ little/ no input from PARASYMPATHETIC div
- the sympathetic NS will trigger vasoconstriction & reduce renal blood flow, reducing urine output
Tubular reabsorption
- nephrons perform after filtration: to MODIFY the filtrate as it flows through tubules
- nephron is able to reabsorb MAJORITY of filtered water & solutes from proximal tubule & loop
Tubular secretion
- process where stubstances are added into filtrate from peritubular capillaries for excretion from body
- helps maintain ELETROLYTE & ACID-BASE HOMEOSTASIS, REMOVES TOXINS from blood that did not enter tubular fluid by filtration
Glomerular filtration
Process of nephrons → selectively filter blood (by size)
FENESTRATED ENDOTHELIUM
- 70-700 nanometre pores - exclude blood cells
BASAL LAMINA (basement membrane) ECM gel
FENESTRATION SLITS (visceral layer)
Forces that drive fluid movement:
- HYDROSTATIC PRESSURE (BP): force on capillary walls
- COLLOID OSMOTIC PRESSURE → created by proteins
interaction vetween these two pressures determines NET FILTRATION PRESSURE and direction that water will flow
Autoregulation GFR - Tubuloglomerular Feedback
Glomerulus receives feedback on status of downstream tubular fluid
- juxtaglomerular apparatus afferent arterioles makes contact w/ ascending limb loop of henle
- tubule comes to contact w/ afferent & efferent arterioles @ vascular poles of renal corpuscle
Autoregulation GFR- myogenic mechanism
Reult of inherent tendency for arterioles to contract/ dialate in response to changes in BP
- inc. arterial BP stretches the different arteriole which stimulates muscle cells to contract
- when BP falls, afferent arteriole relaxes & allows blood flow
- filtration remains stable
Juxtaglomerular apparatus
Juxtaglomerular cells: found in afferent arteriole → act as mechanoreceptors
- able to secrete renin when there is a drop in GFR which regulates systemic BP via RAAS
Macula Densa Cells: found in distal tubule → acts as chemoreceptors
tubuloglomerular feedback
- High GFR
- high rate of flow of filtrate through the nephron
- when flow of filtrate is too fast, decreased reabsorption of ions in tubules
- increase osmolarity (NaCl) in filtrate passing through Distal Tubule
- detected by macula densa cells of distal tubule. → release vasoconstrictor
- afferent arteriole constricts, decreasing blood flow through glomerulus
- GFR returns to normal
- Filtration flow rate decreases
Renin-angiotensin-aldosterone system (RAAS)
- complex system that maintains systemic BP primarily and GFR secondarily
- resonds to combination of three conditions: stimulation by sympathetic nervous system, low glomerular hydrostatic pressure, and stimulation from macula densa
Atrial Natriuetic peptide (ANP)
- hormone released by heart cells in ATRIA in resonse to increasing fluid vol
- lowers blood vol & BP to reduce workload of the heart
Central neural regulation of GFR
involves SYMPATHETIC DIV of ANS and hormone → ANOREPINEPHRINE
- inc sympathetic activity causes constriction of afferent arterioles
→inc systemic BP
- low levels of sympathetic stimulation trigger JG cells to release renin
- high levels of sympathetic stimulation leads to high levels of angriotensis-II; constricts both afferent and efferent arterioles, decreasing GFR to minimise fluid loss, preserve blood vol and maintain BP
endocrine regulation of tubular absorption - Antidiuretic hormone (ADH)
- released by post, part of pituitary gland
- increases water reabsorption in collecting ducts
endocrine regulation of tubular absorption - aldosterone
- secreted by adrenal glands
- acts on collecting ducts and distal convoluted tubules
- Na+ reabsorption water flows
- decreases K+ levels
endocrine regulation of tubular absorption - Parathyroid hormone
- secreted by the parathyroid glands
- acts on distal convoluted tubule
- increases Ca2+ reabsorption
Counter-current mechanism
ADH increases water reabsorption in LOH, DCT, & CD
- water re-enters the tissue fluid and blood stream
- decreases urine vol
recaptures NaCl and returns it to renal medulla
Descending limb
- reabsorbs water but not salt
- concentrates tubular fluid
ascending limb
- reabsorbs Na+, K+ and Cl-
- maintains high osmolarity of renal medulla
- impermeable to water
- tubular fluid becomes hypotonic
