The Urinary System Chapter 17/26

One of the many functions of the urinary system is to rid the body of waste materials. A human waste product is any substance that has no function, for example, excessive carbon dioxide from cellular respiration, toxic nitrogen-containing molecules from the breakdown of proteins, and uric acid from the breakdown of nucleic acids. Even excess water needs to be removed. Several tissues, organs, and processes of this organ system contribute to the temporary confinement of wastes, transport of waste materials, and excretion of wastes from the body.

Contents:1. Kidney

2. Ureter

3. Urinary Bladder

4. Urethra

Functions:

1. Remove nitrogenous wastes from blood (produces urine)

2. Storage and removal of urine from body (micturition)

3. Regulation of blood volume

4. Regulation of ions in blood (Na+)

5. Regulation of blood pH (H+)

6. Participation in Vitamin D metabolism. (converts precursor into active form)

7. Hormone secretion (endocrine organ)

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1. Kidney: general information

paired, bean-shaped organs located in superior and posterior corner of abdominal region (*not cavity).

About 4-5 inches long, 2-3 inches wide, 1 inch thick.

An adrenal gland lies at superior end of each kidney.

Right kidney slightly more inferior than left, due to presence of liver.

On medial side of each kidney is a depression (hilum or hilus pl)

Technically, kidneys lie exterior to abdominal cavity. Lie exterior to parietal peritoneum. *retroperitoneal

hormones secreted: 1. Erythropoietin – stimulates production of new blood cells

2. Renin – regulates blood pressure & kidney function

2. Kidney: external coverings- there are three layers of connective tissue surrounding each kidney:

A. Renal fascia. A thin sheet of dense regular connective tissuea. Function: anchors kidney to posterior abdominal wall

B. Adipose capsule = renal fat pad. Made of adipose tissue. a. Function: protects kidney from physical injury

C. Renal capsule A thin sheet of dense irregular Connective Tissue. Smooth layer resting directly up in kidney tissue

a. Function: protection

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3. Kidney: internal anatomy- 3 major regions:

A. Cortex a. Outer region of kidneyb. Reddish in colorc. Spectrum of cortex tissue. Extend deeper into kidneyd. Renal columns

B. Medullaa. middle region of kidneyb. consists of 8-18 shaped structures (pyramids)c. tip of each pyramid faces inwardd. tip called renal papilla

C. Sinusa. inner region of kidneyb. a space or cavity, not a physical structurec. sinus filled with adipose and renal pelvis

Renal pelvis = expanded and flared out superior end of ureter.

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Minor calyx relatively small spaces that collect drops of urine that flow out of renal papillae

Major calyx relatively large spaces that collect drops of urine from several minor calyses (2-3/kidney)

4. Renal blood vessels http://www.youtube.com/watch?v=lfGYd1wrTgE

Each minute, about 20% of all oxygenated blood leaving the heart goes to both kidneys. Highly vascularA series of decreasing diameter arteries extend deep into each kidney

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a) Renal Arteries – branches off aorta, enter renal sinus at hilum

b) Segmental arteries – up to 6/kidney. Located within renal sinus

c) Interlobar arteries – travel parallel to renal columns

d) Arcuate arteries – arch over the base of pyramid

e) interlobular arteries – small arteries that extend into cortex region

f) afferent arteriole – bring blood to a nephron

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5. Ureter

A pair of muscular tubes that carry urine from kidney to urinary bladder

Each about 10 inches long

Retroperitoneal in location

Superior end is greatly expanded (renal pelvis)

Occupies most of renal sinus in kidney

Lined with transitional epithelium

Stretches and relaxes with flow of urine

Smooth muscle in ureter wall & contracts with peristalsis

Contractions push urine toward bladder

6. Urinary bladder

A hollow muscular sac that temporarily stores urine.

Holds about 700-800 ml

*Retroperitoneal (external to the peritoneal lining of the abdominal cavity)

Lined with: transitional epithelium

Size and location varies with gendero Empty: bladder lies entirely within pelvic cavityo Full: extends superiorly into abdominal cavity to level of umbilicus

At junction with urethra, smooth muscle thickens to form a sphincter: internal urethral sphincter

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7. Urethra

A muscular tube that carries urine from bladder to external environment

Lined with stratified columnar and transitional epithelium

Has two sphincterso Internal urethral sphincter (smooth muscle)o External urethral sphincter (skeletal muscle)

a. Female

About 1-2inches long

Passes through muscular floor of pelvis

Opening to external environment located just superior to vagina

External urethral orifice

b. Male

* About 8-9 inches long

* Passes through muscular floor of pelvis

*Passes through prostate gland and entire length of penis

* Opening to external environment located at tip of penis (external urethral orifice)

Quiz #1

8. Nephron * Functional unit of the kidney*

A microscopic tube in which urine is formed

Over 1 million nephrons per kidney

Lined with simple cuboidal

2 major sections: renal corpuscle and renal tubule

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A. Glomerulus* A small tuft or tangle of capillaries located off the afferent arteriole.

B. Glomerular (=Bowman’s) capsule* A C-shaped tube that surrounds glomerulus (plasma flows into nephron here)

C. Proximal convoluted tubule* Short portion of tubule that has flexures

D. Loop of Henle* Long portion of tubule that dips down into medulla

E. Distal convoluted tubule* Second portion of tubule that has flexures

F. Collecting duct* A central tube that collects urine from many adjacent nephrons

* Empties into minor calyx at renal papilla

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9. Formation of Urine - Three major steps to produce urine

A. Glomerular filtration

Occurs at renal corpuscle (glomerulus and glomerular capsules)

Transfer of plasma (and most all dissolved or suspended materials) from glomerulus into glomerular capsule

Movement occurs without ATP because of force of blood pressure in glomerulus

Fluid (and materials)within nephron = filtrate

Filtrate contains most all common blood components except: formed elements and larger proteins

Glomerular filtration rate (GFR) = the amount of filtrate produced by both kidneys. This is approximately 125 ml/min or 180 L/day.

Summary: A large amount of plasma enters the nephron and becomes filtrate

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B. Tubular reabsorption

Occurs at proximal convoluted tubule and loop of Henle

Movement of needed materials (ex: water, nutrients, ions) from filtrate Back into interstitial fluid blood

About 99% of filtrate actually is returned back into plasma

Some materials simply diffuse, others must use active transport

Remaining 1% of filtrate forms urine.o Contains mostly water, all metabolic wastes, some unneeded ionso About 1.8 L/day produced

Summary:o Most all needed materials and water is returned to blood from filtrate o Waste products and small amount of water in filtrate now called urine.

C. Tubular secretion

Occurs in the loop of Henle and distal convoluted tubule and collecting duct.

The final transfer of nitrogen waste products from blood back into urine.

Movement occurs by active transport, forcing wastes into urine against a concentration gradient.

Hormones that regulate water ions in body influence cells here (aldosterone-salt) (ADH-water)

Summary: final transfer of excess ions and waste products, water back into urine, using ATP.

10. Micturition reflex

Release of urine from urinary bladder into external environment

o Begins with bladder filling up with urine

o Urine pushes against wall of bladder, beginning reflex

o Internal urethral sphincter relaxes

o If person is ready, voluntary relaxation of external urethral sphincter

o Urine exits body by muscular contraction of bladder wall

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11. Disorders of the urinary systemA. Urinary tract infection (UTI)

A bacterial infection of urethra and/or urinary bladder

Infection can spread into kidney, causing loss of kidney function

More common in women

Symptoms: burning /pain on micturitionFrequent micturition

Treatment: Antibiotics

B. Kidney stone

Precipitation of salts within urine into a solid mass within ureter or kidney

If large enough, can block flow of urine in renal pelvis or ureter

Symptoms: severe pain in lumbar region

Treatments: sound-wave therapy, surgery, time (stone wile it on its own)

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