Structure And Functions Of Urinary System

Structure and Functions of the Urinary System

By the end of this session students are expected to be able to:

• Define the Urinary System
• List Structures of Urinary System
• Describe the Structures of the Urinary System

Explain the Functions of the Structures of the Urinary System

Definition of the Urinary System

• What is urinary system?

What are the structures of urinary system?

Structure And Functions Of Urinary System

Urinary system: is the system which regulates the content of blood plasma to maintain the homeostasis of the internal fluid environment within normal limits (control the composition of blood and blood volume) It removes waste products from the blood, of which many of them are toxic The principal organ of the urinary system is the kidney The accessory organs include the ureters, urinary bladder and urethra The following are the (4) structures of the urinary system:

• Kidneys
• Ureters
• Urinary bladder,

Urethra

Structures of the Urinary System

• The kidneys

Are bean shaped organs with a medial indentation located in the upper abdominal cavity on either side of the vertebral column, behind the peritoneum.They typically extend from T12 to L3.The right kidney is slightly lower than the left due to presence of the liver.

Are embedded in adipose tissue that acts as a cushion and is in turn covered by a fibrous connective tissue membrane called the renal fascia, which helps hold the kidneys in place The renal artery enters the kidney, and the renal vein and ureter emerge The outer tissue layer is called the renal cortex, which is made of renal corpuscles and convoluted tubules The inner tissue layer is the renal medulla, which is made of loops of henle and collecting tubules

The renal medulla consists of 6-18 distinct conical or triangular or wedge-shaped structures called renal pyramids.

The tip of each pyramid is its apex or papilla Renal pelvis is a cavity formed by the expansion of the ureter within the kidney at the hilus Funnel shaped extensions of the renal pelvis; called calyces enclose the papillae of the renal pyramids Urine flows from the renal pyramids into the calyces, then to the renal pelvis and out into the ureter Nephron

• Nephron is the structure and functional unit of the kidney
• It is well associated with the blood vessels and the urine is formed there

Each nephron has two major portions: a renal corpuscle and a renal tubule

NEPHRON

Renal corpuscle

Consists of a glomerulus surrounded by a Bowman‘s capsule.

The glomerulus is a capillary network that arises from an afferent arteriole and empties into an efferent arteriole.

The diameter of the efferent arteriole is smaller than that of the afferent arteriole, which helps maintain a fairly high blood pressure in the glomerulus.

• Bowman’s capsule

Is the expanded end of a renal tubule and encloses the glomerulus.

The fluid that is formed from the blood in the glomerulus will eventually become the urine

The renal tubule

Continues from Bowman‘s capsule and consists of the proximal convoluted tubule (in the renal cortex), loop of Henle (in the renal medulla), and distal convoluted tubule (in the renal cortex).

The distal convoluted tubules from several nephrons empty into a collecting tubule.

Several collecting tubules then unite to form a papillary duct that empties urine into a calyx of the renal pelvis.

Blood flow and urine formation

Blood enters the kidney through the renal artery and flows downstream to afferent arterioles and emerge through efferent arterioles, flowing to upper stream to renal veins, and finally to inferior vena cava The formation of urine involves three major processes The first is glomerular filtration, which take place in the renal corpuscles and The second and third are tubular reabsorption and tubular secretion, which take place in the renal tubules.

Accessory organ of the urinary system

Accessory organs of the urinary system are;

The ureters, urinary bladder, and urethra are responsible for the periodic elimination of urine and do not change the composition or amount of urine.

Ureter

Each ureter extends from the hilus of a kidney to the lower, posterior side of the urinary bladder The smooth muscle in the wall of the ureter contracts in peristaltic waves to propel urine toward the urinary bladder.

As the bladder fills, it expands and compresses the lower ends of the ureters to prevent backflow of urine.

Urinary bladder

It is a muscular sac below the peritoneum and behind the pubic bones.

In women, the bladder is inferior to the uterus; in men, the bladder is superior to the prostate gland.

The bladder is a reservoir for accumulating urine, and it contracts to eliminate urine.

The mucosa of the bladder is transitional epithelium, which permits expansion without tearing the lining.

• The bladder wall is lined with smooth muscle called detrusor, which helps contractions

When the bladder is empty, the mucosa appears wrinkled.

Urethra

• Carries urine from the bladder to the exterior

In women, the urethra is 1 to 1.5 inches long and is anterior to the vagina In men it is 7 to 8 inches, the first part being surrounded by prostate gland and the second passes through the cavernous tissue of the penis

Functions of the Structures of the Urinary System

• Functions of the kidney

Filtering of blood

Protein and blood cells are retained in the blood, while a large volume of filtrate is produced Most of the filtrates volume is reabsorbed back into the blood along with useful molecules and ions Small volume of water, metabolic wastes, toxic molecules, and excess ions remain in the filtrates and the result is the formation of urine

2. Regulation of blood pressure

The kidneys regulate blood pressure by adjusting the volume of blood in the body (JUXTA-GLOMERULAR APP.)

• Regulation of blood volume

The kidneys play a major role in controlling the extracellular fluid volume in the body by producing either large volume of dilute urine or small volume of concentrated urine

• Regulation of the plasma electrolytes;
• Examples are sodium and Potassium ions
• Regulation of the pH of the blood;

The kidneys secrete H+ ions to help regulate blood pH and conserve HCO3- to buffer H+

6. Synthesis of Vitamin D;

The kidneys synthesize 1, 25-dihydroxycholecalciferol, which is the active form of vitamin D

• Production of Red blood cells (Epo)
• Excretion of waste products and foreign substances

In form urine

Function of the Ureter

Carries urine from the kidney to the bladder. Muscles in the ureter walls continually tighten and relax forcing urine down this tube Functions of the urinary bladder

• The bladder's walls relax and expand to store urine,
• The bladder's walls contract and flatten to empty urine through the urethra.
• Functions of the Urethra

Squeezes urine out of the bladder.

Key Points

Urinary system is the system which regulates the content of blood plasma to maintain the homeostasis of the internal fluid environment within normal limits (control the composition of blood and blood volume) Structures of the urinary system include:

• Kidneys
• Ureters,
• Urinary bladder,
• Urethra
• Function of the kidneys are:
• Remove liquid waste from the blood in the form of urine
• Keep a stable balance of salts and other substances in the blood

Produce erythropoietin, a hormone that helps your body make red blood cells

Functions of the Ureter are:

Carries urine from the kidney to the bladder. Muscles in the ureter walls continually tighten and relax forcing urine down this tube Functions of the urinary bladder

• The bladder's walls relax and expand to store urine,
• The bladder's walls contract and flatten to empty urine through the urethra.
• Functions of the Urethra

Squeezes urine out of the bladder

Evaluation

• What is urinary system?
• What are the structures of urinary system?

What are the functions of the Kidney?