term test 2 Flashcards
kidney location
- located at dorsal lumbar area outside of the abdomen , between peritoneum and dorsal abdominal muscles outside the peritoneal cavity
- right kidney more cranial than the left in most domestic animals
gross anatomy of kidney
- bean-shaped structure
- in cattle , it is lobulated
- hilus
- renal pelvis
- renal cortex
- renal medulla
- calyx
hilus - kidney
- indented area in medial side
- where ureters , nerves , blood and lymph vessels enter and leave the kidney
renal pelvis - kidney
- funnel-shaped area
- beginning of ureter
- collects urine produced by renal cortex before it travels through the ureter into the bladder
renal cortex and renal medulla - kidney
renal cortex ;
- outer portion of kidney
renal medulla ;
- inner portion around renal pelvis
calyx / calyces - kidney
- cup-like structure
- formed when renal pelvis extends into the medulla pyramid
- directs and collects fluids into renal pelvis
microscopic anatomy of kidney
- basic functional unit : nephron
each nephron consists ;
- renal corpuscle
- proximal convoluted tubule (PCT)
- loop of henle (LOH)
- distal convoluted tubule (DCT)
renal corpuscle -> PCT -> LOH -> DCT -> urine
- some parts of a nephron eg renal corpuscle are only in the cortex while others eg loop of henle is only in the medulla
renal corpuscle
- located in renal cortex
- glomerulus / glomerular tuft ; cluster of capillaries
- bowman’s capsule ; surrounds the glomerulus to hold the capillaries
- capsular space / bowman’s space ; between capsule and glomerulus , there is a space
- filters blood in the first stage of urine formation
- fluid that is filtered OUT of blood through capillaries and into capsular space = glomerular filtrate
blood supply into glomerulus
- renal artery enters kidneys at the hilus , dividing into smaller arteries and even smaller arterioles
- afferent glomerular arterioles carries blood into glomerular capillaries of renal corpuscle
- glomerular capillaries filters some plasma out of the blood into the bowman’s space and it becomes glomerular filtrate
- efferent glomerular arterioles receives blood from glomerular capillaries
- A goes in , E goes out
proximal convoluted tubule (PCT)
- continuation of capsular space
- twisting path through the cortex
- when glomerular filtrate enters the PCT from the capsular space , it becomes tubular filtrate
- where 65% of reabsorption takes place
loop of henle (LOH)
- long , u-shaped portion of the tubule
- descends from PCT into medulla (descending LOH)
- turns and heads upwards back into the cortex (ascending LOH)
distal convoluted tubule (DCT)
- DCT is the continuation of the ascending LOH
- DCT of all nephrons will drain urine into collecting ducts
- collecting ducts carries tubular filtrate (which is now waste products only / urine) through the medulla and empties into renal pelvis
- primary site of action of ADH (antidiuretic hormone)
reabsorption in the tubules is possible because …
- efferent glomerular arterioles divide to form peritubular capillaries (small capillaries that surround the tubules)
- allows oxygen supply to the tubules , tubular reabsorption , tubular secretion
- peritubular capillaries will converge at the end to form a larger vein (renal vein)
- renal vein leaves the kidney at the hilus to join the caudal vena cava
3 steps of urine formation
- kidney filters unwanted substances to excrete them
1. glomerular filtration
2. tubular reabsorption
3. tubular secretion
glomerular filtration
- glomerular capillaries are permeable (not enough to allow blood cells and large proteins to pass through)
- plasma proteins and substances such as calcium that are bound to them are unable to pass
- fluids leave bloodstream into capsular space
- in glomerular capillaries , blood pressure is very high and forces some plasma out into capsular space
- glomerular filtrate = primitive urine (first stage)
glomerular filtrate
- fluid that passes through glomerular capillaries into capsule space
- any product that is smaller than plasma protein or freely dissolved in plasma appears in glomerular filtrate
- eg sugars , amino acids , toxins
- glomerular filtrate in the capsule space will move on to the next section of the renal tubule (proximal convoluted tubule PCT)
reabsorption
- ensures the body gets back small useful molecules from the filtrate
- eg amino acids , peptides , glucose , water , Na+ , Cl-
- substances to be reabsorbed pass through the tubular lumen , tubular wall and capillary wall back into the bloodstream
- 65% of reabsorption takes place in the PCT , and remaining in the DCT / LOH
- 80% of water , sodium chloride & bicarbonate are reabsorbed
- 100% of glucose & amino acids are reabsorbed [if they are detected in the urine , it could suggest problems]
sodium / glucose & amino acid / potassium & calcium / chloride / water reabsorption
sodium ;
- PCT , LOH , DCT
glucose & amino acid ;
- PCT
potassium & calcium ;
- PCT
chloride ;
- diffuses through in response to an imbalance created by sodium reabsorption
- moves with sodium
water ;
- follows ions through osmosis
- once sodium , glucose , amino acids & chloride have left tubular filtrate , water molecules follow
antidiuretic hormone (ADH) - urinary
- ADH from pituitary gland
- acts on DCT to promote water reabsorption
- tells DCT to reabsorb more water
- concentrates urine
- released when an animal is dehydrated or hypotensive to increase water content in the blood
alosterone
- from adrenal cortex
- acts on DCT to increase reabsorption of sodium
- tells DCT to reabsorb more sodium
- more sodium reabsorbed = osmotic imbalance = water molecules follow
- concentrates urine
- Na+ reabsorbed = K+ secrete
- if sodium is taken in, must be replaced by potassium to maintain salt balance
tubular secretion
- substances from blood capillaries move into tubules / urine
- substances not filtered in the glomerulus eg urea , ammonia OR due to reabsorption of sodium eg potassium , hydrogen for salt and acid-base balance
- occurs in PCT , LOH and DCT
renin - osmoregulation
- hormone secreted in glomerulus in response to low arterial pressure
- if pressure is low , glomerulus cannot filter blood to form glomerular filtrate
- converts angiotensinogen into angiotensin
angiotensin - osmoregulation
- vasoconstriction to raise blood pressure
- the constriction stimulates the release of aldosterone from adrenal cortex , causing water to be reabsorbed into the bloodstream
- more water = higher pressure = glomerulus able to filter blood to form glomerular filtrate
ureters
- leavers kidney at the hilus
- has 3 layers :
1. outer fibrous
2. middle smooth muscle (propels urine by peristaltic contractions)
3. inner layer lined with transitional epithelium (allows ureters to stretch as urine passes through) - enters urinary bladder at oblique angle , forming a valve to prevent back flow
- when bladder is full , urine presses on the entrance to close the valve