Renal system anatomy:

Introduction:

Function of the urinary system:

1. Regulation of blood ionic composition: Na+, Ca2+, Cl-, HPO42-

2. Regulation of blood pH: kidneys excrete H+ to urine and conserves bicarbonate ions

3. Regulation of blood volume: by conserving /eliminating water in urine

4. Enzymatic regulation of blood pressure: kidneys secrete the enzyme renin, which indirectly causes an increase in blood pressure 5. Maintenance of blood osmolarity

6. Production of hormones: calcitriol (active form of vitamin D that regulates calcium homeostasis) and erythropoietin (stimulates production of RBC)

7. Regulation of blood glucose level

8. Excretion of wastes and foreign substances: ammonia, urea, bilirubin, creatinine, uric acid, and other foreign substances * renal system is composed of

Consists of 2 kidneys, 2 ureters, 1 urinary bladder, and 1 urethra. >> so although it does a big job but has few organs

Filtration (functional part ) Conductive part

Kidney : deals with a huge amount of blood & discards waste products through the urethra as urine.

-Ureter: collecting tube, it has nothing to do with reabsorption and filtration.

-Urinary bladder: muscular organ located in the pelvic region that has a certain capacity for the filling of urine. When certain distension is reached, urine must be evacuated.

-Urethra: evacuates & takes urine, under control of human. Urine is discarded though the urethra. The remaining water and solutes (urine), passes through the ureters, is stored in the urinary bladder until it is removed from the body through the urethra.

The kidneys do the major work of the urinary system; the other organs (ureters, urinary bladder, and urethra) function as

*urine composition is not changed as it passes through the conductive part of the urinary system

Location of the kidney :

-The kidneys extend approximately from the level of the 12th thoracic vertebra to the third lumbar vertebra in the posterior abdominal wall

-They receive some protection from ribs

Both kidneys are in direct contact with an important endocrine gland located at the apex (upper part of kidney). Because they are above the kidney, these glands are called suprarenal gland. This gland has no relationship with the kidney function-wise. It’s just located above the kidney but does not function with it.

The purple arrow is adipose capsule

external anatomy :

-The right lies somewhat lower than left as it is positioned under right lobe of the liver which is much larger than

the left lobe

-The adult kidney weights about 150 g

-Dimensions are 12 cm long, 6 cm wide, 3 cm thick

-Medial surface has a vertical cleft called the renal hilus

-Atop each kidney is an adrenal gland which is unrelated to kidney function

- 3 layers of tissue surround kidney:

1.renal capsule (dense irregular connective tissue),

2. adipose capsule (fatty tissue),

3. renal fascia (dense irregular connective tissue)

all important for protection and for holding the kidney in its place.

hilum

Internal anatomy : -Cortex and medulla are the major constituents of the kidney!

-The renal cortex is light in color(pale) and has a granular appearance

- Deep to the cortex is the renal medulla

-Darker tissue which exhibits cone shaped tissue masses called medullary or renal pyramids

-Each renal pyramid has a base which is convex, and a apex which tapers toward its apex or papilla

The apex, or papilla, points internally

-The pyramids appear striped because they are formed almost entirely of roughly parallel bundles of urine collecting tubules called medullary rays

-Inward extensions of cortical tissue called renal columns separate the pyramids so the renal column is

Hilus or hilum : vertical cleft or slit at the center of the medial border in which

the blood vessels , the ureter , the lymphatics , the nerves pass to the kidney

Pyramids

Renal

columns

The papilla is the tip of the renal pyramid that opens into

the minor calyx

renal columns: portions of renal cortex that extend between renal

pyramids

-Each medullary pyramid is surrounded by a capsule of cortical tissue to form a lobe

-renal lobe: renal pyramid + renal cortex + half of each adjacent renal column

- parenchyma: renal cortex + renal pyramids (functional portion of kidney)

* the urine will flows from the medulla to the minor calyces >> major calyces >> renal pelvis > ureter >bladder > urethra

Blood supply :

-The kidney continuously cleanse the blood and adjust its composition

-Kidneys possess an extensive blood supply

-Under normal resting conditions, the renal arteries deliver approximately one-fourth (20%-25%) of the total systemic cardiac output to the kidneys each minute >> about 1200 ml/min is delivered to the kidney - the blood come from the renal artery > The right renal artery is longer than the left renal artery and right renal vein is shorter than left renal vein - Because the position of the aorta is more to the left (medial) and the vena cava is on the right side the length

lobe

- A vessel coming from aorta to the right must be longer. And a vessel going from the left to the inferior vena cava should be long

- Each renal artery divides into five segmental arteries that enter the hilus

Each segmental artery divides into lobar and interlobar arteries

The kidney has important subdivisions of vessels that reach the nephrons, specifically the Bowman’s capsule.

- Starting from renal pelvisthe large artery entering the renal pelvis is the renal artery from the aorta. It will subdivide into lower upper, middle arteries segmental arteries.

- In between the large lobes (medullary pyramids) is where the segmental arteries will passinterlobar arteries.

- At the base of the pyramid is the area of contact between cortex and medulla.

-They run in an arch manner arcuate arteries.

- arcuate artery at the cortico-medullary junction -From the arcuate arteries, smaller branches go in to the small lobulesinterlobular arteries. (

cortical radiate arteries)

-From the interlobular arteries, more arteries will appro ch the

Bowman’s capsule afferent arteries.

-When they approach the Bowman’s capsule it breaks into capillaries (glomerular capillaries). - the glomerular capillaries drain into the efferent arteriole - effereret arterioles give peritubular capillary network

-Peritubular arteries unite to form peritubular venules *Venous drainage :

Cortical radiate veins receives blood from the vasa recta (capillaries and extensions of efferent arterioles >interlobular veins > arcuate veins >interlobar veins > renal vein>inferior vena cava

*the blood supply starts form renal artery >> segmental artery that enter the hilus >> lobar arteries >interlobar arteries > arcuate arteries> interlobular arteries >> afferent arteriole>> glomerular capillaries >> efferent arterioles

-The renal arteries issue at right angles from the abdominal aorta

The nephron : - Each kidney contains over 1 million tiny blood processing units called nephrons, which carry out the processes that form urine >> so they are the functional units

- In addition, there are thousands of collecting ducts, each of which collects urine from several nephrons and conveys it to the renal pelvis

-located in the parynchema

- During a single day, all nephrons will filter 180 L fluid , so there is a continuous process of filtration in kidney; -blood goes to kidney several times a day so that waste products can be filtered & excreted outside of body as urine. To conclude, the nephron is the most important structure in the cortex that regulates these vital functions.

Parts of the nephron :

Each nephron consists of the renal corpuscle (where blood plasma is filtered) and the renal tubule (where the filtered fluid passes)

Part details

Renal corpuscles

*it’s composed of two parts :

1- glomerulus : it’s a tuft of capillaries arise from the afferent arteriole

-The capillaries in the glomerulus are surrounded by 2 arterioles, whereas the capillaries of the body are surrounded by an arteriole and a venule.

2-bowman’s capsule :- it’s cup shaped structure surrounds the glomerulus

- it’s doubled layered

-Consists of visceral and parietal layers -Visceral layer: simple squamous epithelial cells called PODOCYTES. They wrap around the endothelial layer of glomerular capillaries and form the INNER wall of the capsule.

-Parietal layer: simple squamous epithelial cells that make up the OUTER wall of the capsule.

- receives filtered fluid from capillaries

- the most proximal part of the nephron

- all glomeruli and bowman’s capsules lie in the cortex

Proximal convoluted tubule

-travels in a long time in a short space and is very close to the Bowman’s capsule - receive the filtered fluid from renal corpuscle - it lies in the cortex

Loop of henle - This loop has both an ascending and descending limb -extend to the medulla ,especially in the juxtamedullary nephron

Distal convoluted tubule

-continue and take the fluid from the loop of henle -lies in the cortex

Collecting ducts

*At the end of the distal convoluted tubule, there will be no reabsorption at all. –What remains left is the urine, which will be discarded out of the body. -In the end of the distal convoluted tubule, urine is collected by a series of ducts until it reaches the apex of the medullary pyramid, then to the renal pelvis ureterurinary bladder urethra -lie in the medulla mainly

Some notes : 1-the filtered fluid pass through capillaries >Proximal convoluted tubule Loop of Henle Distal convoluted tubule. 2-

-Normally there should be no blood in urine because if the kidney is functioning normally and efficiently, it will receive a huge

amount of blood and reabsorb it. It will then discard the filtrate into the collecting duct as urine, which should not have blood or proteins.

-However, there may be pathological lesions causing blood and proteins in the urine, caused by a defect in the nephronshematuria / proteinuria .

-Limited amount of nephrons are functioning normally. In certain tumors, half of a kidney can be removed and the human can still live normally. There is a huge reserve of nephrons in both kidneys. 3-nephrons are 2 types : - cortical

cortical juxtamedullary 80-85% 15-20%

Short loops in the cortex Long loops extend to the medulla

Peritubular capillaries Vasa recta

Ureter :

- begins at the pelvis of the kidney (medial cavity), where medulla terminates .

-Each leaves the renal pelvis, decends behind the peritoneum(retroperitoneal) to the base of the bladder, turns and then runs obliquely through the medial bladder wall .

-The ureters are protected from a backflow of urine because any increase within the bladder compresses and closes the ends of the ureters

*Histologically, the walls of the ureter is trilayered(3 layers)

-An inner layer of transitional epithelium lines the inner mucosa

-The middle muscularis layer is composed of a an inner longitudinal layer and an outer circular layer

-The outer layer is composed of fibrous connective tissue

-The ureters play an active role in transporting urine

-Distension of the ureters by incoming urine stimulates the muscularis layer to contract, which propels the urine into the bladder

-The strength and frequency of peristaltic waves are adjusted to the rate of urine formation

Urinary bladder :

*it’ a storage organ It can expand for storage or collapse when empty, that receives the urine from ureters > and empties into the urethra

- In females, the bladder is anterior to the vagina and uterus

- In males, the bladder lies immediately anterior to the rectum

-The interior of the bladder has openings for both ureters(ureter opening) and the urethra(intenal urethral sphincter )

*it had a body and neck

The triangular region of the bladder base outlined by these openings is called the trigone which is a common site of infections

Distension does not occur in the trigone, even if the urinary bladder is full. It will remain fixed in shape so that it doesn’t close the openings of the ureter

The smooth muscles of the bladder forms folds , but at the area that connect the ureter openings and urethra

> it become smooth and called the trigone

*The bladder wall has three layers

1- A mucosa containing transitional epithelium that’s stratified which is unique

2- A thick muscular layers

3- A fibrous adventitia

*The muscle layer consists of smooth muscle arranged inner and outer longitudinal layers

Collectively the muscle layer is called the detrusor muscle (literally to thrust out The bladder is very distensible and uniquely suited for its function of urine storage)

-Empty its walls are thick and thrown into folds (rugae) and found in the pelvis

-As it expands it becomes pear shaped and rises in the abdominal cavity

-The bladder can store more than 300 ml of urine without a significant increase in internal pressure

-A moderately full bladder holds approximately 500 ml

-Urine is held in the bladder until release is convenient

Urethra:

-The urethra is a thin muscular tube that drains urine from the bladder and conveys it out of the body

-Urethra is different in both sexes.

male female

the external urethral orifice is at the tip of the penis. It also passes through the prostate gland and prostatic urethra. The external urethral orifice is at the tip of the penis & is longer.

-The male urethra has two basic functions *It carries urine out of the body

*It carries semen into the female reproductive tract

the external urethral orifice opens in the vulva inside the vagina. The urethra is shorter, and has several advantages.

Male urethra > prostatic , membranous , penile(spongy)

So the major differences in the urinary systems of males and females are located in the external urethral orifice of the urethra.

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- Stone formation is more likely to occur in males because of the constrictions in the male urethra. It rarely occurs in females.

-These crystals may also be collected during the filtration of blood.

Notes :

-Can kidneys be removed? Yes! If there is a certain pathology/tumor in body OR in kidney donation.

-Can the suprarenal gland be removed? No! It must always be kept in the body because of its high importance.

Done by : majd alahmad

Because of the filtration of huge amount of blood passing through the kidneys, certain crystallized materials will also pass. These crystallized materials can either be beneficial or useless. If they are useless, they must be excreted with urine. If they are not excreted and stay within the bladder for a long time, they will eventually accumulate . this explains why the urinary system is susceptible to stone formation (accumulation of crystals).

-Sometimes, these stones pass with urine out of the body without being felt. Other times, they will remain in the pelvis of the kidney, ureter, bladder, or in urethra