Biology: Urinary System Ch 5-2

• The urinary system is covered in Chapter 5-2 of a general biology course for the 2025 1st semester
• The lecture is given by 박수연 PhD. RN from 건양대학교

Learning Objectives

• Describe the structure and function of the urinary system
• Understand the regulatory actions of urination
• Understand renal function regulation and homeostasis mechanisms
• Recognize diseases related to the urinary system

Urinary System

• The urinary system is also known as the excretory system
• Ammonia (NH3) is created in the liver through amino acid decomposition
• It is toxic and so has to be quickly expelled from the body

Ammonia Toxicity

• Ammonia (NH3) is created in the liver by breaking down amino acids
• Ammonia is toxic and needs to be excreted from the body quickly
• Hyperammonemia is a common symptom of liver failure

Symptoms of Hyperammonemia:

• General symptoms are growth retardation and hypothermia
• Central symptoms are aggressiveness, lethargy, and coma
• Eye symptom is papilledema
• Muscular/neurologic symptoms include poor coordination, dysdiadochokinesia, hypotonia/hypertonia, ataxia, tremor, seizures, decorticate/decerebrate posturing
• Pulmonary symptom is shortness of breath
• Liver symptom is Enlargement

Diagram of Urea Creation

• The healthy liver converts ammonia into urea
• The kidneys remove urea from the body
• Liver failure results in toxic accumulation of ammonia which then is circulated to the brain leading to coma and death

Excretory Organs

• Cells produce metabolic waste that must be excreted to maintain homeostasis
• Both mammals and amphibians convert ammonia to urea
• Urea is less toxic than ammonia

Major Metabolic Waste Products

• Protein becomes amino acids, which become amino groups (-NH2)
• Nucleus acids become Nitrogenous bases

Nitrogenous Waste Metabolism

• Ammonia (NH3) is very toxic
• Urea is less toxic than Ammonia
• Uric Acid are not toxic but do not dissolve in water so precipitate as crystals

Gout

• Caused by an increase of uric acid produced by the decomposition of nucleotides (DNA, RNA) in the liver
• Uric acid crystals accumulate in blood vessels and joints, causing pain
• It is caused by overproduction or insufficient excretion of uric acid

Excretory System

• The excretory system includes the kidneys, ureters, bladder and urethra
• The kidney is also known as the renal
• Refer to figure 8-2

Bladder and Urethra

• Refer to figure 8-3

Waste Removal

• Humans have several systems responsible for removing waste
• The urinary system is one of the most vital

Components and Function

• Kidneys remove waste from blood, regulate water levels and blood pressure, and maintain blood pH.
• Ureters transport urine to the bladder.
• Bladder stores urine and contracts for urination.
• Urethra transports urine out of the body.

Structure and Function

• The urinary system (urinary tract, renal system) excretes various metabolic waste products through urine
• The bladder consists of the kidneys and the excretory canal

Multiple Regulatory Functions

• Maintains fluid homeostasis by controlling salt and water levels in urine
• Excretes metabolic waste products, such as urea and uric acid
• Regulates electrolyte concentrations like inorganic salts, acids, and bases
• Regulates pH levels
• Secretes renin, which regulates blood pressure
• Secretes erythropoietin to regulate red blood cell production
• Secretes hormones that stimulate calcium absorption in the intestine

Nephrons

• Blood enters the kidneys through the renal artery
• Renal arteries divide into millions of nephrons
• The nephron is kidney's fundamental unit which includes glomeruli, Bowman's capsule, and renal tubules.
• Nephrons create urine
• Urine travels from the kidneys using the ureter and into bladder
• Urine releases through the urethra

Kidney Function

Nephron Filtration

• Filtration happens in the glomerulus into the bowman's capsule
• The process filters out small material
• Including water, glucose, urea, inorganic salts, and amino acids

Reabsorption

• Occurs in the renal tubule to the capillaries
• Absorbs material that the body needs
• Like water and glucose

Secretion

• Occurs in the capillaries to the renal tubule
• Secretes any waste that is still in the blood
• Like urea

Anti-Diuretic Hormone (ADH)

• Water loss decreases blood volume and increases blood osmotic pressure
• osmoreceptors detects osmotic pressure change and stimulates the release of anti-diuretic hormone
• ADH increases water reabsorption which increases blood volume and lowers osmotic pressure

Aldosterone

• Aldosterone is a hormone secreted by the adrenal cortex to maintain water balance
• Renin reacts with angiotensinogen to produce angiotensin I (inactive)
• Another enzyme converts angiotensin I to angiotensin II (active)
• Angiotensin II raises blood pressure by causing vasoconstriction
• Adrenal glands are stimulated to secrete aldosterone
• Aldosterone increases sodium reabsorption
• Increased blood volume reduces renin secretion

Caffeine and Ethanol

• Caffeine increases blood pressure in glomeruli, increasing water excretion from blood
• Ethanol inhibits ADH secretion in the pituitary gland, reducing water reabsorption

Urinary System Diseases

• This includes kidney stones, refer to figure 8-8

Kidney Failure Treatments

• Hemodialysis: Cleaning the blood artificially
• Peritoneal Dialysis: Infusing dialysate fluid to filter waste by osmosis and diffusion

Diabetes Insipidus

• Caused by an antidiuretic hormone (ADH) deficiency or defects in ADH action in the kidneys, leading to imbalances in water metabolism
• Characterized by excessive urination, thirst, frequent urination, nocturia, and bed-wetting