Test 3

A&P 2 Test #3 Study Notes (October 22nd, 2025)

Topics Covered

  • Components of the Urinary System

  • Kidney Anatomy & Physiology

  • Nephron: Microscopic Functional Unit of the Kidneys

  • Carbohydrates: Glycogen, Starch, and Cellulose

  • Adenosine Triphosphate (ATP): Energy Currency for All of Life

Components of the Urinary System

  • The urinary system comprises:

    • Two kidneys

    • Two ureters

    • One bladder

    • One urethra

  • The adrenal glands are located superior to the kidneys but are part of the Endocrine System, not the urinary system.

Kidney Functions

  • Function of the Kidneys:

    • Filter the blood to maintain homeostasis by detecting and directing changes in blood concentrations.

  • Blood Flow:

    • Whole blood enters the kidneys via renal arteries from the aorta.

    • Blood does not need to be oxygenated for kidney function.

Blood Pressure Generation for Filtration

  • Pressure is critical for the filtration process in the kidneys, generated in two ways:

    1. Aorta Pressure: Blood exits the aorta under high pressure due to left ventricular contraction.

    2. Glomerular Pressure: Blood enters the glomerulus via the afferent arteriole, which has a larger diameter compared to the efferent arteriole (5 times wider), creating pressure differences in the glomerulus.

Nephrons: Filtering Units

  • Nephron Function:

    • Filtering occurs in nephrons located in the renal cortex; about one million nephrons are present in each kidney.

  • Filtration Process:

    • Whole blood enters the nephron through the afferent arteriole into the glomerulus, a rolled-up capillary bed.

    • The filtration membrane consists of:

    • Endothelial cells of the glomerulus

    • Podocytes

    • Only plasma passes through the filtration membrane forming filtrate captured in Bowman’s capsule.

Renal Tubule Structure

  • Structure:

    • The renal tubule connects to Bowman’s capsule and consists of:

    • Proximal convoluted tubule (PCT)

    • Loop of Henle

    • Distal convoluted tubule (DCT)

  • Peritubular Capillary Network:

    • Surrounds the renal tubule and consists of oxygenated and deoxygenated blood, aiding in nutrient absorption/reabsorption.

Urine Formation Process

  • Filtrate Processing:

    • The filtrate moves through the renal tubule where kidney cells determine what substances re-enter the blood (peritubular capillaries) and which are excreted (renal tubule).

  • Collecting Duct:

    • Filtrate (now urine) is concentrated by water reabsorption into the bloodstream before being channeled into the ureters.

  • Urine Transportation:

    • Urine travels from the kidneys to the bladder via peristalsis and gravity.

Homeostatic Functions of the Kidneys

  • Maintaining Blood Pressure:

    • The kidneys manage blood volume by secreting or reabsorbing sodium (Na+), which regulates blood pressure directly.

    • Increased blood volume leads to increased blood pressure and vice versa.

  • Impact of Ethanol:

    • Alcohol consumption can impede the normal mechanisms of blood volume regulation, leading to dehydration.

  • Diuretics:

    • Substances that increase urine output, affecting blood pressure and leading to potential hypotension and tachycardia.

Electrolyte and Acid-Base Balance

  • Electrolyte Regulation:

    • The kidneys regulate sodium (Na+), potassium (K+), calcium (Ca2+), chloride (Cl-), and phosphate (HPO4^2-).

    • Maintenance of blood osmolarity: optimal range of approximately 290 mOsm/L.

  • pH Balance:

    • Normal blood pH is between 7.35 to 7.45.

  • Acidosis: Excess H+ leads the kidneys to excrete H+ and generate bicarbonate (HCO3^-).

  • Alkalosis: Lack of H+ leads the kidneys to reabsorb H+ and excrete HCO3^-.

Hormonal Functions of the Kidneys

  • Erythropoietin (EPO):

    • Secreted when oxygen levels are low, stimulating red blood cell production from hematopoietic stem cells in the bone marrow.

    • Constant secretion, with variation based on oxygen needs; crucial for patients on dialysis.

  • Renin:

    • Enzyme released when blood pressure falls, triggering the RAA pathway to increase Na+ reabsorption, blood volume, and blood pressure without altering heart function.

Waste Excretion

  • Excretion of Metabolic Wastes:

    • Kidneys remove excess nitrogenous wastes (ammonia, uric acid, creatinine, and urea) produced during metabolism.

  • Glomerular Filtration Rate (GFR):

    • Normal GFR is 100-125 mL/min. A GFR of 50-60 mL/min indicates kidney dysfunction, often asymptomatic in chronic kidney disease

Chronic Kidney Disease (CKD)

  • Consequences:

    • Leads to accumulations of toxic waste within the body; often undiagnosed until serious symptoms present.

  • Over 90% of individuals with CKD are unaware of their condition, particularly if they also have high blood pressure or diabetes.

Carbohydrates Overview

  • All carbohydrates consist of linked glucose subunits; the primary forms include:

    • Starch

    • Glycogen

    • Cellulose (Note: Humans lack the enzymes to digest cellulose).

  • Glucose Usage:

    • Glucose is pivotal for ATP production, and fluctuating blood glucose levels must be managed through diet or glycogen breakdown.

ATP Structure and Function

  • ATP:

    • Composed of adenine, ribose, and three phosphate groups; energy is released by breaking the terminal phosphate bond yielding ADP (adenosine diphosphate).

  • ATP Cycling:

    • Energy is utilized as ATP converts to ADP, with glucose intake facilitating the re-synthesis of ATP.

Diabetes Overview

  • Types of Diabetes:

    • Type 1: Autoimmune destruction of pancreatic β-cells, requiring insulin injections.

    • Type 2: Insulin resistance, linked to obesity; management focuses on lifestyle modifications.

  • Consequences of Impaired Glucose Transport:

    • Both types lead to starvation at the cellular level with risks of increased fatty acid metabolism, circulatory complications, and organ damage.

Pancreatic Functions

  • Anatomy:

    • Located on the left side of the abdomen

  • Digestion:

    • Produces inactive digestive enzymes and bicarbonate to neutralize stomach acid, ensuring optimal pH in the small intestine.

  • Hormonal Regulation:

    • Insulin and glucagon are key hormones managing blood glucose levels antagonistically.

Chromosomal Insights

  • Human Chromosomes:

    • Humans have 23 chromosomes, with 1-22 being autosomes and one sex chromosome (X or Y).

    • Males are XY, females are XX; all human somatic cells are diploid while gametes are haploid.

  • Impact of Age on Chromosome Quality:

    • Maternal and paternal ages affect genetic health outcomes; older age increases risks for chromosomal abnormalities.

Female Reproductive System

  • Ovarian Function:

    • Involves monthly ovulation; fertilization typically occurs in the fallopian tube, leading to implantation in the uterus.

  • Ectopic Pregnancy:

    • A rare and significant risk where implantation occurs outside the uterus, potentially leading to severe complications.

  • Endometriosis:

    • Aberrant growth of endometrial tissue in pelvic cavity due to hormonal influences; management considerations include hormonal therapies.

Gender Determination

  • Factors influencing gender determination involve:

    • Genetic contributions from sex chromosomes,

    • Maternal and fetal hormonal signals,

    • Proper hormone receptor functionality in target cells.