Renal system Flashcards
What is the function of the kidneys?
Excretery organs - process blood and rid the body of the waste products of metabolism via urine
What do the kidneys maintain homeostasis of?
Fluid Electrolytes (sodium/potassium) Acid/base Blood pressure Calcium/vitamin D Erythropoietin
What are the components of the urinary system?
Two kidneys (produce urine)
Ureters (Convey urine)
Bladder (stored)
Urethra (void urine)
What are the three distinct parts of the kidney?
- Cortex - 85% of nephrons
- Medulla - urine is concentrated, prevents excessive water loss
- Pelvis - collection area for urine which is funneled into ureter
What are the blood vessels of the kidney?
Renal artery delivers blood from abdominal aorta
Renal artery Segmental arteries Lobar arteries Interlobar arteries Arcuate arteries Interlobular arteries
How does blood move from the interlobular arteries to the interlobular veins?
Blood travels through afferent arterioles to the glomerular capillaries and then out via efferent arterioles to peritubular capillaries and finally interlobular veins
What are the veins of the kidney?
Interlobular veins Arcuate veins Lobar veins Segmental veins Renal vein Inferior vena cava
What is a nephron?
A structure optimally evolved to filter blood plasma
and excrete waste products of metabolism in urine
What are the two types of nephrons?
Cortical
Juxtamedullary
What is the renal corpuscle?
The blood filtering component of the nephron
Consists of:
Glomerulus
Bowmans capsule
What is the renal tubule?
The renal tubule is the part of the nephron involved in reabsorption and secretion.
It consist of:
- PCT
- Loop of Henle
- DCT
After passing through the renal tubule, the filtrate continues to the collecting duct system.
What is the glomerulus?
A network of fine capillaries
Single layer of endothelial cells surrounded by basement membrane
Enables rapid filtration of blood plasma
Surrounded by bowmans capsule
What is the bowmans capsule?
A cuplike structure surrounding the glomerulus
Parietal (outer) layer
Visceral (inner) layer comprised of specialised epithelium - Podocytes
What forms the filtration barrier in the renal corpuscle?
The glomerular endothelium, basement membrane and pedicels of the podocytes
Filtration barrier freely permeable to water and small molecules but NOT large protein or cells
How is filtration controlled in the filtration membrane?
Filtration is facilitated by a pressure gradient - hydrostatic pressure
What is filtered from the plasma?
Sodium Chloride Calcium Phosphate Potassium Bicarbonate Water Glucose Amino acids Urea Creatinine
What is not filtered in glomerulus?
Cells Large proteins (haemoglobin) Negatively charged proteins (albumin)
What is the glomerular filtration rate?
The rate at which blood is filtered through the glomerulus into the Bowmans capsule
What drives GFR?
Glomerular hydrostatic pressure
What counteracts GFR?
Hydrostatic pressure in bowmans capsule or glomerular osmotic pressure
What factors can influence GFR?
- Hydrostatic pressure
- Osmotic pressure
- Systemic blood pressure
- Renin-angiotensin system
- Disease
Normal healthy GFR = 125ml/min
What does a reduced GFR result in?
Inefficient blood clearance and waste removal
What can be used to estimate GFR?
Serum creatinine (and urea) measurements
What GFR is indicative of kidney failure?
Less than 15%
What facilitates reasborption?
Sodium transport facilitates reabsorption of nutrients, water and ions
What facilitates secretion?
Sodium transport facilitates secretion of H_ (and waste)
Where does reabsorption occur?
Within the renal tubule
65% in PCT
25% in ascending LofH
8% reabsorbed in DCT
How much sodium is reabsorbed?
98%
How does water move?
Via aquaporins
How do glucose and amino acids move?
Via sodium cotransporters
How does reabsorption occur in the PCT?
Sodium/potassium pump 3 na out/2 k in Na moves against conc gradient Everything (almost) follows Na - Water - Glucose and amino acids co-transported with Na - Chloride
Remaining filtrate continues to LofH
What features of the nephron lie in the cortex?
PCT
DCT
Renal corpuscle
What features of the nephron lie in the medulla?
Loop of Henle
collecting duct too but not part of nephron technically
Is the descending limb of the LofH thin or thick?
Thin - freely permeable to water
Is the ascending limb of the LofH thin or thick?
Both - has two sections
Thin part impermeable to water but permeable to ions
Thick part impermeable to water
Actively pumps na, cl, and k into interstitium
Interstitium becomes ‘salty’
Generates osmotic gradient
Facilitates water reabsorption from thin ascending limb
What is the vasa recta?
It maintains the concentration gradient of the medulla
What is the concentration of solutes in the plasma?
Approx 300 mosm/kg
How is the 200 mOsm/L difference between interstitual fluid and the ascending limb created?
Movement of sodium ions out
Does the osmolarity increase or decrease due to a loss in sodium?
Decreases
What happens after sodium is pumped out of the thick ascending limb?
After 200 mOsm/L gradient established, water moves passively out of the thin descending limb until equilibrium reached between interstitial fluid and filtate.
Water moving out descending limb doesn’t affect ISF osmolarity but lowers the filtrate osmolarity.
What is the maximum osmolarity?
1200 mOsm/L
Tubule fluid entering the distal convoluted tubule is?
Hypotonic with the interstitium
What is the purpose of distal convoluted tubule?
Fine-tuning - site of fluid volume and electrolyte regulation
Sodium and water reasbsorption hormonally regulated
- ADH - increases water reasborption
- Aldosterone - Increases Na reabsorption
- Atrial natiuretic hormone (ANH) - Promotes Na secretion
What are the juxta-glomerular apparatus and what is their function?
Macula densa - detects sodium conc
Juxtaglomerular cells - adjust the diameter of the afferent arteriole
What occurs in normal homeostatic blood pressure?
GFR in normal limits as is sodium conc
Macula dens detects this and does not pass signal to juxtaglomerular cells thus large diameter of afferent arteriole and thus GFR is maintained
What occurs from elevated BP in tubuloglomerular feedback?
Elevated systemic BP leads to elevated glomerular hydrostatic pressure increasing GFR and sodium conc in DCT, detected by macula densa which signals to juxtaglomerular cells to constrict via release of adenosine - lowers GFR by reducing blood flow
What occurs from decreased BP in tubuloglomerular feedback?
Macula densa detects drop in sodium conc and releases prostaglandins which act on juxtaglomerular cells to cause dilation of afferent arterioles, only has marginal effect
Main response - release of RENIN from juxtaglomerular cells in response to prostaglandins
How does the renin angiotensinogen-system work?
Angiotensinogen released into circulation
Renin converts angiotensinogen to Angiotensin 1
Angiotensinogen coverting enzyme converts angiotensin 1 into angiotensin 2
Angiotensin 2 is a potent vasoconstrictor - rapidly increases blood pressure
What is Angiontensin 2 detected by?
Adrenal medulla- release of aldosterone
Hypothalamus - release of ADH
What does Atrial Natriueretic peptide do?
Helps to return an elevated blood pressure to homeostasis by inhibiting the action of renin, aldosterone and ADH.
Promotes water and sodium excretion
How does RAAS raise blood pressure?
Via Angiotensin II
How does RAAS raise blood volume?
Via aldosterone and ADH
What are the symptoms of chronic kidney disease?
Nausea Oedema Blood/protein in urine Anaemia Weak/painful bones
What are the causes of CDK?
Hypertension
Diabetes
High cholesterol
Long term use of NSAIDs
How do you regulate hypertension?
Diet
Diuretics
ACE inhbitors inhibit angiontensin II
Beta-blockers block SNS by stress hormones
What receptor facilitates sodium reabsoprtion of apical membrane?
NKCC2
What is dialysis and what are the two types?
Dialysis is the artifical removal of wastes, solutes, water and toxins from blood
Haemodialysis
Peritoneal dialysis
Required in stage 5 (kidney failure)
