Urinary System

what is the urinary system

major excretory system of the body

although kidneys are categorizes as excretory organs, what else are they important for

many metabolic activities

what are the functions of the kidneys

- excretion

- regulation of blood volume and pressure

- regulation of blood solute concentration

- regulation of extracellular fluid pH

- stimulation of RBC synthesis

- activation of vitamin D

what are the major ions the kidneys regulate

Na, Cl, K, Ca, HCO3-, HPO4 2-

where are the kidneys located

retroperitoneal in non-mesenteric region and on each side of the vertebral column near psoas major muscle

what do the kidneys secrete to secrete RBC production

erythropoietin

what causes the right kidney to be slightly lower

the liver

what is each kidney surrounded by (from kidney -> outer)

- an outer layer of CT = renal capsule

- a layer of adipose tissue for protection

- the renal fascia to anchor the kidneys to the abdominal wall

- more adipose tissue

what is the hilum continuous with

adipose and CT-filled cavity = renal sinus

what is the renal hilum

area where structures enter and exit the kidney, then pass through the renal sinus

what are the structures in the hilum

- renal artery and nerves enter

- renal vein and ureter exit

what is the renal medulla composed of

many renal pyramids which project into the cortex, AKA medullary rays, and the apex of the pyramid are the renal papilla

what are the renal columns

part of cortical tissue that extends into medulla between pyramids and their medullary rays

what do the renal pyramids do

they are a collection of tubes and ducts that transport fluid throughout the kidney and modify it into urine, then transport it towards renal sinus

what does the minor vs. major calyx do

urine from the renal papilla emptys into the minor calyx, and the urnie from several minor calyxes empty into major calyx

what do the major calyxes converge to form

renal pelvis

how many minor calyxes vs. how many major calyxes in each kidney

8-20 that converge to form 2-3

what is the renal pelvis

funnel-shaped tube embedded in and surrounded by renal sinus and narrows into the ureter

what is the renal sinus

fat filled space surrounding renal pelvis and vessels

what is a nephron

functional unit of the kidney

what are the 4 segments of a nephron

- renal corpuscle incortex

- PCT in cortex

- loop of henle with sections in cortex and medulla

- DCT in cortex

what do each portion of the nephron do in urine production

- renal corpuscle, filters blood

- PCT, returns filtered substances to blood

- loop of henle, helps conserve water and solutes

- DCT, rids blood of additional waste

what is the pathway of urine produced by a nephron

renal corpuscle -> PCT -> loop of henle -> DCT -> collecting duct -> renal papilla -> papillary duct -> minor calyx -> major calyx -> renal pelvis

what is the papillary duct

merger of several collecting ducts into the large tubule that empties into a minor calyx

juxameduallary nephron

renal corpuscles near cortical medullary border and nephron loops extend deep into medulla

cortical nephron

renal corpuscle closer to periphery of cortex and nephron loops do not extend deep into medulla

what type of nephron is the majority

cortical

what is the filtration part of a nephron called

renal corpuscle

what is a renal corpuscle

a network of capillaries twisted around each other = glomerulus

what are the parts of a renal corpuscle

glomerulus and bowman's capsule

what is the bowmans's capsule

surrounds the glomerulus and is an indented, double-walled chamber

what is filtrate

fluid filtered from the glomerulus

where does fluid from the bowman's capsule then flow to

PCT

what are the layers of the bowmen's capsule

- outer layer/parietal layer made up of simple squam.

- inner later/visceral layer made up of podocytes

where does the simple squam. epithelium of the parietal layer change and what does it change to

it becomes cube-shaped where PCT begins

what do the podocytes do

Create filtration slits in the glomerulus

how does blood flow through the glomerulus

Blood enters through the afferent arteriole and exits through the efferent arteriole

what is the juxaglomerular apparatus

a structure that consists of specialized cells of the afferent arterioles of the renal corpuscle (juxaglomeruluar cells) and special cells of the DCT (macula densa cells)

what fenestrae in the glomerulus

openings in the endothelium of glomerular capillaries from the podocytes

what can NOT fit through fenestrae

large proteins and blood cells

what are filtration slits

gaps between the cell processes of the podocytes of the visceral layer

what is the filtration membrane

consists of capillary endothelium, basement membrane, and podocytes and forms the first major step in urine production where the fluid from blood moves across the membrane into the lumen of the bowmen's capsule

what are 3 characteristics of the renal corpuscle for filtration

porous capillaries, porous visceral layer, and high pressure

how do the glomerular capillaries have a higher pressure

bc the efferent arteriole leaving the corpuscle has a smaller diameter than the afferent arteriole entering

what is the function of the juxtaglomerular apparatus

the site of renin production = role in regulation of filtrate formation and BP

what are the sections of the renal tubule in order of urine formation

1. PCT

2. descending loop of henle

3. ascending loop of henle

4. DCT

5. collecting ducts

what is the wall of the PCT composed of

simple cuboidal epithelium with many microvilli

what forms the outer surface of the PCT

it resting on a basement membrane

what does every loop of henle have

- descending limb that is very similar to PCT and becomes very thin as it extends into the medulla

- ascending limb that abruptly switches to simple squamous and begins thin but thickens and become simple cuboidal as it returns toward renal corpuscle and ends by transitioning to DCT

how does the DCT compare to the PCT

not as long but still simple cuboidal just smaller cells and do not have many microvilli

what is the collecting duct

form from many DCT and composed of simple cuboidal

how is the collecting duct different from the rest of the nephron

larger in diameter that other segments

what do collecting ducts form

medullary pyramids

what parts make up a nephron

renal corpuscle and renal tubule

renal artery

branch from abdominal aorta and form segmental arteries

interlobar arteries

branch from segmental arteries and ascend within renal columns toward cortex

arcuate arteries

branch from interlobar arteries and arch over base of renal pyramids

cortical radiate arteries/interlobular arteries

branch from arcuate arteries into the cortex

afferent arterioles

derived from interlobular arteries or their branches that carry blood to glomerular capillaires

glomerular capillaries

site of filtration

efferent arterioles

arise from glomerular capillaries and carry blood away from renal corpuscle

peritubular capillaries

efferent arterioles give rise to this plexuses of capillaries around PCT and DCT

vasa recta

specialized set of peritubular capillaries associated with the juxaglomerular nephrons

what do the peritubular capillaries then drain into (and so on...)

interlobular veins that then drain into arcuate veins, then interlobar veins, and finally the renal vein

what does the renal vein then do once it exits the kidney

connects to inferior vena cava and blood returns to the heart

what is the order of arteries and veins in order (all of them)

renal arteries -> segmantal arteries -> interlobar arteries -> arcuate arteries -> interlobular/cortical radiate arteries -> afferent arterioles -> glomerular capillaries -> efferent arterioles -> peritubular capillaries -> interlobular veins -> arcuate veins -> interlobar veins -> renal veins

what are the 3 major steps of urine formation

1. glomerular filtration

2. tubular reabsorption

3. tubular secretion

general info about filtration

BP forces the fluid and small moleculed out of the blood and is non-selective = separates based only on size or charge of the molecule

what is important to remember about filtration

it does not remove everything in the blood, only substances small enough to fit through the filtration membrane

what does the renal tubule contain to aid in tubular reabsorption

many transport proteins that move water and some filtrated molecules back into the blood to prevent them from being lost

what generally occurs during tubular secretion

Certain two wall cells will transport additional solute from the blood into the filtrate, but they may not have been filtered by the filtration membrane

What does urine consist of

Substances filtered directly from the blood and secreted directly from the blood into the renal tubule, minus any reabsorbed substances

What is filtration

A nonspecific process where materials are separated based on size or charge

What is the importance of filtration indicated by

The large percentage of total cardiac output, or blood, that is sent through that is sent through the kidneys = renal fraction

What are 2 standard measures of kidney function that is often used by health professionals

renal blood flow rate and renal plasma flow rate

What is glomerular filtration rate

volume of filtrate formed per minute by both kidneys

What is the filtration membrane

Within the renal corpuscle and allows water and small molecules to leave the blood while preventing blood cells and most proteins from leaving the blood

What is the principle component of the filtration membrane

The glomerulus

So with the filtration membrane, does that mean the filtrate is protein free

No, it's still contains a small percentage of protein

What happens to any protein that is filtered

It is actively reabsorbed by endocytosis and metabolize by the cell in the PCT

What is one requirement for all filters

A force to enhance movement through it

For the filtration membrane, what are the 3 forces/pressures that determine the amount of filtrate formed

1. Glomerular capillary pressure (GCP)

2. Capsular hydrostatic pressure (CHP)

3. Blood colloid osmotic pressure (BCOP)

What is the combination of the three pressures needed to form filtrate called

Filtration pressure

What is filtrate and is it considered urine

Water, small molecules, and ions that can pass through the membrane and no it is the essential first step

What is the importance of filtration pressure?

It is the pressure gradient responsible for filtration

what is the glomerular capillary pressure (GCP)

an outward pressure from blood pressing on capillary walls = simple means blood pressure

what does the GCP pressure do to the fluids

forces fluids and solutes out of the blood and into bowman's capsule

what is the capsule hydrostatic pressure (CHP)

inward pressure that opposes filtration bc of the force of filtrate volume on the wall of bowman's capsule = pressure of filtrate already in the lumen

what does the GCP roughly =

50 mmHg

what does the CHP roughly =

10 mmHg

what is the average BCOP roughly =

30 mmHg

what is blood colloid osmotic pressure (BCOP)

also an inward pressure that opposes filtrate due to plasma proteins in glomerular capillaries which draws fluid back into glomerulus from bowman's capsule

where is the BCOP greater

at end of glomerular capillary than at the beginning bc of fluid leaving the capillaries and entering the lumen

how is filtration pressure calculated (the actual equation)

GCP (50) - CHP (10) - BCOP (30) = 10 mmHg

what kind of net pressure is the filtration pressure

a net outward pressure

why does it make sense for the colloid osmotic pressure in Bowman's capsule is normally close to zero

the filtrate does not exert an osmotic force on the plasma bc its solute concentration is very low from the few proteins that cross the membrane (protein is the reason for water reabsorption which creates pressure)

what occurs in glomerular nephritis

the filtration membrane becomes more permeable which allows more protein than normal to enter the filtrate -> elevates colloid osmotic pressure = elevates filtration pressure and therefore increases filtrate volume

what does high glomerular capillary pressure result from

- low resistance to blood flow in afferent arterioles

- low resistance to blood flow in glomerular capillaries

- high resistance to blood flow in efferent arterioles

the GFR is very ...

stable -> it does not change significantly even if systemic BP drops very low or raises very high

what is the regulation of the GFR due to

autoregulation