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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 UNIT B Chapter 13: Urinary System Section 13.1 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. urinary system: a type of organ system containing the kidneys, the urinary bladder, and the tubes that carry urine; eliminates metabolic wastes from the body and helps regulate the fluid balance and pH of the blood excretion: the removal of metabolic wastes from the body urine: liquid waste produced by the kidneys and excreted from the body TO PREVIOUS SLIDE

Functions of the Urinary System UNIT B Chapter 13: Urinary System Section 13.1 Functions of the Urinary System Excretion of Metabolic Wastes The kidneys excrete metabolic wastes (mostly nitrogenous wastes: urea, ammonium, creatinine, uric acid) Urea is formed when ammonia released during amino acid breakdown combines with CO2 Some ammonia (NH3) is excreted as ammonium ion (NH4+) Creatinine is a breakdown product of creatine phosphate, a high-energy phosphate reserve molecule 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 urea: a by-product of amino acid metabolism ammonia: a product of the breakdown of amino acids in the liver; extremely toxic uric acid: produced by the breakdown of nucleotides gout: a painful ailment caused by too much uric acid in the blood, which forms crystals and precipitates out in the joints TO PREVIOUS SLIDE

UNIT B Chapter 13: Urinary System Section 13.1 Osmoregulation The kidneys are involved in osmoregulation (maintenance of the balance of water and salt in the blood) 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 (HCO3-), and calcium (Ca2+), in the blood Regulation of Acid-Base Balance The kidneys help regulate the acid-base balance of the blood Monitor and keep blood pH at 7.4 by excreting hydrogen ions (H+) and reabsorbing bicarbonate ions (HCO3-) osmoregulation: the maintenance of the appropriate balance of water and salt in the blood TO PREVIOUS SLIDE

UNIT B Secretion of Hormones Chapter 13: Urinary System Section 13.1 Secretion of Hormones The kidneys help the endocrine system in hormone secretion 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 Secrete the hormone erythropoietin (EPO) to simulate red blood cell production when oxygen demand increases Help activate Vitamin D, a hormone-like molecule that promotes calcium (Ca2+) absorption from the digestive tract erythropoietin (EPO): a hormone secreted by the kidneys that stimulates red blood cell production TO PREVIOUS SLIDE

Organs of the Urinary System UNIT B Chapter 13: Urinary System Section 13.1 Organs of the Urinary System The urinary system consists of the kidneys, ureters, urinary bladder, and urethra. 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. TO PREVIOUS SLIDE

UNIT B Chapter 13: Urinary System Section 13.1 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 kidneys: paired organs of the urinary system that regulate the chemical composition of the blood and produce a waste product called urine TO PREVIOUS SLIDE

UNIT B Chapter 13: Urinary System Section 13.1 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 ureters: small, muscular tubes that conduct urine from the kidneys to the bladder TO PREVIOUS SLIDE

Urinary Bladder UNIT B Stores urine until it is expelled from the body Chapter 13: Urinary System Section 13.1 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 External sphincter is under voluntary control urinary bladder: part of the urinary system that stores urine until it is expelled from the body TO PREVIOUS SLIDE

UNIT B Chapter 13: Urinary System Section 13.1 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) urethra: a small tube that extends from the urinary bladder to an external opening that removes urine from the body; in the male reproductive system, it connects to the ejaculatory ducts TO PREVIOUS SLIDE

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

Check Your Progress UNIT B Define excretion. Chapter 13: Urinary System Section 13.1 Check Your Progress Define excretion. Describe the functions of the urinary system. Describe a function of the kidneys. ANSWERS 1. Excretion is the removal of liquid metabolic wastes. 2. The four major functions of the urinary system are excretion of wastes, maintenance of water–salt balance (osmoregulation), maintenance of acid–base balance, and secretion of hormones. 3. The kidneys produce urine, which contains metabolic wastes such as urea and uric acid, and maintain osmotic balance, blood volume, blood pressure, and acid–base balance. The kidneys also produce renin and erythropoietin and activate vitamin D. TO PREVIOUS SLIDE

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

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