Urinary System Flashcards
What are the dimensions of the average adult kidney?
Depth - 3cm
Length - 11cm
Width - 6cm
Weight - 150g
Describe the anatomy of the kidney
- Renal tubule lined with epithelial cells
- PCT has dense microvilli to increase SA
- Macula densa cells are chemoreceptors
- Glomerulus lines with endothelium which is adapted with fenestrations to make it porous
What are the 7 functions of the kidneys?
- Water regulation
- Maintains BP
- Gets rid of waste products
- Activates vit. D (helps body absorb Ca)
- Acid-base balance
- Maintains electrolyte balance, critical for heart rhythm
- Releases erythropoietin which causes bone marrow to make RBC
What is one of the causes of high BP?
High water levels in blood
How much of the cardiac output goes through the kidneys?
25% (1200ml)
Show the flow of blood through the renal blood vessels
- Aorta
- Renal artery
- Segmental artery
- Interlobar artery
- Arcuate artery
- Cortical radiate artery
- Afferent glomerular arteriole
- Glomerulus
- Efferent glomerular arteriole
- Peritubular capillaries and vasa recta
- Cortical radiate vein
- Arcuate vein
- Interlobar vein
- Renal vein
- Inferior vena cava
What are the nephron-associated blood vessels
- 2 capillary beds of nephron = glomerulus and peritubular/ vasa recta
- Renal plexus - provides nerve supply to kidneys and ureter
- Sympathetic vasomotor fibres - regulate blood flow by adjusting diameter of the renal arterioles
What are the functions of the glomerulus and vasa recta?
Glomerulus = filtration
Vasa recta = selective reabsorption
Describe the juxtaglomerular apparatus
- Found at the distal end of the ascending limb of the loop of Henle, lying against the afferent arteriole
- Regulates filtration and maintains systemic BP
What is glomerular filtration?
Movement of water and solutes from an area of high pressure to an area of low pressure
(Forced through capillary walls and pores of glomerulus into Bowman’s capsule)
Describe the process of glomerular filtration
- High BP in the glomerulus forces water and solutes across the filtration membrane
- Filtrate consists of water and small molecules
- Large molecules and blood cells do NOT enter the Bowman’s capsule
- The kidneys filter the body’s entire plasma volume 60 times each day
What is the filtration membrane?
Pores of glomerulus and walls of Bowman’s capsule
Name 5 small molecules in filtrate
- Glucose
- Vitamins
- Amino acids
- Waste substances
- Electrolytes
What is glomerular filtration rate?
The amount of filtrate formed by both kidneys each minute
Volume formed in adult kidneys = 120-125ml/min
What is GFR determined by?
- SA
- Filtration membrane permeability
- Net filtration pressure
What are the 2 mechanisms that control GFR?
- Intrinsic control
2. Extrinsic control
Describe intrinsic control
- Autoregulation
- Macula densa cells control degree of arteriole constriction by responding to Na levels and releasing a vasoconstricting chemical that acts on the afferent arteriole
- This system maintains a constant GFR over an arterial pressure range of 80-180mmHg
Describe extrinsic control
Norepinephrine released by sympathetic NS
Epinephrine released by adrenal medulla
This causes:
- Afferent arteriole constriction
- Inhibits filtration
- Release of renin which participates in the RAAS
What is the RAAS?
Renin Angiotensin Aldosterone System
Describe the effect of BP on arterioles
High BP = constriction of afferent arterioles and dilation of efferent arterioles
Low BP = dilation of afferent arterioles and constriction of efferent arterioles
Describe the RBC through the kidneys
- Flow through renal artery to afferent arteriole
- In glomerulus, they stay within blood and exit via efferent arteriole
- Squeeze through peritubular capillaries
- Travel through vasa recta where absorbed substances from nephron flow in via osmosis and active transport
- Peritubular capillaries in venules meet and reach renal veins where they exit kidney and flow back to heart
How much of the body does water make up?
Infant - 70%
Child - 65%
Adult - 60%