1. Chapter 10: Urinary System and Excretion

2. The Urinary System The major roles of the urinary system are:
Maintaining homeostasis in blood of salt, water, and pH.
Removal of metabolic wastes from the body.
This process is called excretion.

3. Four Functions of the Urinary System
 Excretion of Metabolic Wastes
The most notable metabolic wastes kidneys excrete are nitrogenous wastes. The primary one is urea and three others are ammonium, uric acid, and creatinine.
 Maintain Water-Salt Balance
Kidneys maintain appropriate water-salt balance of blood to cause osmosis, the diffusion of water. This has the kidneys involved with regulating blood pressure.

4. Four Functions of the Urinary System
  Maintain Acid-Base Balance
Kidneys monitor and help control blood pH by mainly excreting hydrogen ions to keep a 7.4 blood pH.
  Secretion of Hormones
Kidneys assist the endocrine system by secreting the hormones: Erythropoietin, Calcitriol, and Renin.

5. Organs of the Urinary System
The urinary system organs consists of the: kidneys, ureters, urinary bladder, and urethra.

6. Kidney Location
The bean-shaped kidneys are located near the small of the back, on either side of the vertebral column.

7. Organs of the Urinary System
The kidneys are covered by a tough tissue called the renal capsule.
The concave side of a kidney has a depression where the renal artery enters and the renal vein and ureter exit the kidney.

8. Two small muscular tubes called ureters conduct the urine from the kidneys to the urinary bladder for storage. Two sphincter muscles are located at the bottom opening of the bladder, allowing it to retain urine.

9. Urination – Figure 10.2

10. Urination
The inner sphincter is involuntarily controlled and the outer external sphincter can be voluntarily controlled.
With maturation, the brain controls this reflex and delays urination, until a suitable time.

11. Urination
As the bladder fills with urine, stretch receptors in its muscle layers send sensory nerve signals to the spinal cord and impulses return that cause the bladder to contract and sphincters to relax, so that urination can occur.
A small tube called the urethra carries urine from the bladder to an external opening.

12. Kidney Structure A kidney has three major regions inside:
The Renal cortex,
Renal medulla, and
Renal pelvis.
The “functional units of excretion” are the microscopic tubules called nephrons.
A kidney is composed of over one-million nephrons that produce urine.

13. Blood Supply in a Kidney

14. Anatomy of a Kidney

15. Kidney Diagram – Figure 10.3

16. Anatomy of a Nephron Each nephron has several parts.
Glomerular capsule (Bowman’s capsule)
Closed cuplike end, lined with squamous cells.
Proximal convoluted tubule
Twisted part of tube, closest to the capsule.
Loop of the nephron (loop of Henle)
Descending narrow tube that makes a U-turn.
Distal convoluted tubule
Twisted part of tube further from the capsule.
Collecting duct
Larger tubule several nephrons finally enter.

17. Parts of a Nephron Proximal Distal Convoluted Tubule Convoluted Tubule
Collecting
Duct
Glomerulus
Capsule
Nephron Loop

18. Blood Supply of a Nephron
Each nephron has its own blood supply.
A wider afferent arteriole carries blood into the glomerular capsule, where it divides to become a knot of capillaries called the glomerulus.

19. Blood Supply of a Nephron
Each nephron has its own blood supply.
An efferent arteriole carries blood out of the glomerular capsule. An important feature here is the narrower efferent arteriole which increases pressure. The efferent arteriole then branches into the peritubular capillary network, surrounding the nephron.
Blood then enters a venule
that carries blood into the renal vein.

20. Nephron Anatomy

21. Urine Formation Glomerular filtration Tubular reabsorption
Urine is 95% water and 5% solids (urea, salts, bicarbonate ions).
Urine formation is divided into three steps.
Glomerular filtration
Tubular reabsorption
Tubular secretion

22. Urine Formation

23. Glomerular Filtration
Small molecules: including water, nutrients, salts, and nitrogenous wastes are forced by pressure out of the blood inside the glomerulus (capillaries) and into the glomerular capsule.
Blood cells, platelets, and plasma proteins are too large and unable to pass through the capillary walls.
About 180 liters of water are filtered daily.

24. Tubular Reabsorption
Certain nutrients, water and some urea move from the nephron tubules back into the blood of the peritubular capillary network. Almost all glucose and amino acid molecules re-enter the blood from the proximal convoluted tubules.
Tubular reabsorption is a selective process because only molecules recognized by carrier protein molecules are actively reabsorbed.
The number of carriers limits the rate of this process.

25. Reabsorption from Nephrons

26. Tubular Secretion
Specific substances such as hydrogen ions (H+), creatinine, and drugs such as penicillin move from the blood into the nephron tubules.
In the end, urine contains substances that have undergone glomerular filtration, but have not been reabsorbed and substances added by tubular secretion.

27. Steps in Urine Formation
Figure 10.7

28. Kidneys and Homeostasis
The kidneys play a major role by:
Removing nitrogenous waste such as urea, which is essential to maintaining homeostasis.
Maintaining the salt-water balance of the blood for proper blood volume and blood pressure.
Maintaining the 7.4 blood pH.

29. Water Reabsorption
The antidiuretic hormone (ADH) plays an important role of conserving body water by closing water channels in distal nephron tubules, thus reducing the loss of water in urine.
This hormone is released by the pituitary gland when water intake is low.

30. Kidneys and Homeostasis
Diuretics are chemicals that increase the flow of urine.
Alcohol inhibits secretion of ADH; dehydration after drinking may contribute to the effects of a hangover.
Caffeine increases the glomerular filtration rate and decreases tubular reabsorption of sodium.

31. Kidney Function Disorders
Many types of illness cause progressive renal disease and ultimate renal failure.
Diabetes
Hypertension
Inherited conditions
Urinary tract Infections:
Nephritis (Pyelonephritis)
Cystitis
Urethritis
Kidney stones are hard granules of calcium, uric acid, and proteins that form in the renal pelvis.

32. Artificial Kidney Machine
Kidney dialysis requires patients to sit relatively still during a treatment, which often lasts over three hours and is required three to four times a week.

33. Replacing a Kidney
Patients with renal failure sometimes undergo a kidney transplant operation, during which a compatible donor kidney is received.