Chapter 26: Urinary System and Body Fluids

Organs of the urinary system:

Kidneys:

• 2

• produce urine

Organs of the urinary system:

Ureters:

• 2

• transport urine to the urinary bladder

Organs of the urinary system:

Urinary bladder:

• temporary storage of urine

Organs of the urinary system:

Urethra:

• transports urine from the urinary bladder to the exterior of the body

Main functions of the kidneys:

Excretion:

• filter blood and produce a large volume of filtrate

—large molecules are retained in the blood and smaller molecules enter the filtrate

—most of the filtrate is reabsorbed back into the blood

—metabolic wastes, toxic molecules, and excess ions remain in the filtrate and are used for urine production

Main functions of the kidneys:

Regulation of blood volume and pressure:

• play a major role in the regulation of extracellular fluid volume by producing:

—large volume of dilute urine

—small volume of concentrated urine

Main functions of the kidneys:

Regulation of blood ion concentration:

• help regulate the concentration of the major ions such as:

—sodium, calcium, chloride, bicarbonate, potassium

Main functions of the kidneys:

Regulation of pH:

• the kidneys secrete variable amounts of H+ to help regulate the extracellular fluid pH

Main functions of the kidneys:

Vitamin D production:

• regulate the synthesis of vitamin D

—controls blood calcium levels

Main functions of the kidneys:

Erythropoiesis:

• secrete erythropoietin (EPO)

• regulates the synthesis of erythrocytes in the bone marrow

Describe the location and external anatomy of the kidneys:

Retroperitoneal:

• Located posterior to the parietal peritoneum near the posterior abdominal wall on each side of the vertebral column

• lumbar vertebrae and rib cage partially protect

• R kidney slightly lower than left

—bean shaped

—approximately fist sized

External anatomy of the kidney:

Renal capsule:

**outer membrane

• fibrous connective tissue that surrounds the exterior of the kidney

Perirenal fat:

• thick layer of adipose tissue surrounds the renal capsule and is held in place by the renal fascia

—thin layer of CT that help anchor the kidneys and fat to the abdominal wall

Hilum:

• small area on the medial side of each kidney where blood vessels, nerves, and uterus enter and exit

Structure and function of the inner regions of the kidney:

Renal cortex:

outer layer of kidney

Renal medulla:

inner layer of the kidney

Renal pyramids:

• cone shaped and located between the renal columns

—bases from the boundary between the cortex and medulla

Renal columns:

• extensions of the renal cortex into the medulla between the renal pyramids

Renal papillae:

• located at the apex of the renal pyramid

Renal sinus:

*Tip of columns

• cavity at the tip of the renal column is filled with adipose tissue, loose connective tissue, and blood vessels

Minor calyces:

-funnel-shaped chambers into which the renal papillae extend

• each kidney contains 8-20

• minor calyces of several pyramids merge to form major calyces

Major calyces:

-Larger funnels

• each kidney contains 2-3

• converge to form enlarged chamber called the renal pelvis

**collect urine from minor calyces

Renal pelvis:

• enlarged chamber

• collects urine from the major calyces

• narrows into a small-diameter tube called the ureter

Ureter:

• small- diameter tube that exits the kidney at the hilum and connects to the urinary bladder

Nephron:

**actually produces urine

• functional unit of kidney

• ~1.3 mil in each kidney

• includes: renal corpuscle, proximal convoluted tubule, loop of henle, and the distal convoluted tubule

Pathway of urine flow from the collecting ducts to the ureter:

• nephron

• collecting ducts

• papillary ducts

• renal papillae

• minor calyces

• major calyces

• renal pelvis

• ureters

Parts of a renal corpuscle:

Bowman’s capsule:

• the enlarged end of the nephron surrounding the glomerulus (ball of yarn)

• filtration occurs here:

—fluid leaves the blood in the glomerulus and enters Bowman’s capsule and then flows into the proximal convoluted tubule

Parts of a renal corpuscle:

Glomerulus:

• network of capillaries

• blood enters through afferent arteriole, exits through efferent arteriole

Parts of a nephron:

*Bowman’s capsule:

• has an outer parietal layer and an inner visceral layer consisting of podocytes (foot processes)

Parts of a nephron:

Fenestrae:

*window-like pores in the endothelium of the glomerular capillaries

Parts of a nephron:

Filtration slits:

• gaps between the cell processes of the podocytes

Parts of a nephron:

Filtration membrane:

• capillary endothelium

• basement membrane

• podocytes

Cortical nephrons:

• 85% of total nephrons

• located in the cortex

Juxtamedullary nephrons:

• located at the cortex- medulla junction

• have loops of henle that deeply invade medulla

• have extensive thin segments

• involved in the production of concentrated urine

Glomerulus: Circulation

1) Afferent arteriole

2) Efferent arteriole

1) Drains glomerulus

2) supplies glomerulus

Blood supply of the nephron (Kidneys: Circulation)

Afferent arterioles:

—> then glomerulus

• carry blood to the glomerulus

Efferent arterioles:

• carry blood away from the glomerulus

Peritubular capillaries:

• surround the proximal and distal convoluted tubules

Vasa recta:

• specialized parts of peritubular capillaries extend deep into the medulla and surround the loop of henle