UNIT B: Human Body Systems Chapter 8: Human Organization Chapter 9: Digestive System Chapter 10: Circulatory System and Lymphatic System Chapter 11: Respiratory System Chapter 12: Nervous System Chapter 13: Urinary System: Section 13.1 Chapter 14: Reproductive System

13.1 The Urinary System The urinary system is involved in excretion, which is the removal of metabolic wastes from the body. The urinary system produces urine and conducts it outside the body. UNIT B TO PREVIOUS SLIDE Section 13.1 Chapter 13: Urinary System

Functions of the Urinary System Excretion of Metabolic Wastes The kidneys excrete metabolic wastes (mostly nitrogenous wastes: urea, ammonium, creatinine, uric acid) o Urea is formed when ammonia released during amino acid breakdown combines with CO 2 o Some ammonia (NH 3 ) is excreted as ammonium ion (NH 4 + ) o Creatinine is a breakdown product of creatine phosphate, a high-energy phosphate reserve molecule o Uric acid is produced from the breakdown of nucleotides −Gout can occur if too much uric acid in the blood has crystallized and moved into the joints UNIT B TO PREVIOUS SLIDE Section 13.1 Chapter 13: Urinary System

Osmoregulation The kidneys are involved in osmoregulation (maintenance of the balance of water and salt in the blood) o Salts can cause osmosis (diffusion of water) into the blood, causing blood volume and blood pressure to increase Kidneys also maintain levels of other ions, such as potassium (K + ), bicarbonate (HCO 3 - ), and calcium (Ca 2+ ), in the blood Regulation of Acid-Base Balance The kidneys help regulate the acid-base balance of the blood o Monitor and keep blood pH at 7.4 by excreting hydrogen ions (H + ) and reabsorbing bicarbonate ions (HCO 3 - ) UNIT B TO PREVIOUS SLIDE Section 13.1 Chapter 13: Urinary System

Secretion of Hormones The kidneys help the endocrine system in hormone secretion o Secrete renin, an enzyme that stimulates the adrenal cortex to secrete the hormone aldosterone, which promotes the absorption of sodium ions (Na + ) by the kidneys o Secrete the hormone erythropoietin (EPO) to simulate red blood cell production when oxygen demand increases o Help activate Vitamin D, a hormone-like molecule that promotes calcium (Ca 2+ ) absorption from the digestive tract UNIT B TO PREVIOUS SLIDE Section 13.1 Chapter 13: Urinary System

Organs of the Urinary System The urinary system consists of the kidneys, ureters, urinary bladder, and urethra. UNIT B TO PREVIOUS SLIDE Figure 13.1 The urinary system. Urine is found only within the kidneys, the ureters, the urinary bladder, and the urethra. The kidneys are important organs of homeostasis because they excrete metabolic wastes and adjust both the water–salt and acid– base balance of the blood. Section 13.1 Chapter 13: Urinary System

Kidneys Paired, bean-shaped organs that regulate acid-base balance and water-salt balance of blood Each kidney is covered by a tough connective tissue layer called a renal capsule Each kidney has a depression (called a hilium) on the concave side where a renal artery enters and a renal vein and ureter exit UNIT B TO PREVIOUS SLIDE Section 13.1 Chapter 13: Urinary System

Ureters Small muscular tubes that transport urine from the kidneys to the bladder Wall of each ureter has three layers: inner mucosa, smooth muscle layer, outer fibrous connective tissue Peristaltic contractions in the ureters cause urine to enter the bladder UNIT B TO PREVIOUS SLIDE Section 13.1 Chapter 13: Urinary System

Urinary Bladder Stores urine until it is expelled from the body Has three openings: two for the ureters, and one for the urethra, which drains the bladder Has two sphincters that lie close to where the urethra exits the bladder o External sphincter is under voluntary control UNIT B TO PREVIOUS SLIDE Section 13.1 Chapter 13: Urinary System

Urethra Small tube opening that extends from the bladder to an external opening Removes urine from the body Males: 20 cm long; urethra carries urine and semen Females: 4 cm long; urethra carries urine (not connected to reproductive system) UNIT B TO PREVIOUS SLIDE Section 13.1 Chapter 13: Urinary System

Urination When the bladder fills with about 250 mL of urine, stretch receptors send nerve impulses to the spinal cord Motor nerve impulses from the spinal cord cause the bladder to contract and sphincters to relax, allowing urination to occur The brain controls this reflex in older children and adults, allowing urination to be delayed UNIT B TO PREVIOUS SLIDE Figure 13.2 Urination. As the bladder fills with urine, sensory impulses go to the spinal cord and then to the brain. When urination occurs, motor nerve impulses cause the bladder to contract and internal and external sphincters to relax. Section 13.1 Chapter 13: Urinary System

Check Your Progress 1.Define excretion. 2.Describe the functions of the urinary system. 3.Describe a function of the kidneys. UNIT B TO PREVIOUS SLIDE Section 13.1 Chapter 13: Urinary System

UNIT B TO PREVIOUS SLIDE Section 13.1 Chapter 13: Urinary System

UNIT B TO PREVIOUS SLIDE Section 13.1 Chapter 13: Urinary System