Nervous, Urinary, and Reproductive Systems Overview

Overview of the Nervous System

• Definition and General Purpose: The nervous system is a regulating system that functions to maintain homeostasis. It utilizes electromechanical impulses to gather information about external and internal environments. While some activities are conscious, most occur without awareness.

• Primary Functions:

  • Detection: To detect environmental changes and feel sensations.

  • Response: To initiate appropriate responses to those changes.

  • Organization: Organize information for immediate use and store it for future use.

  • Cognition/Senses: Provide the capacity to see, hear, talk, feel, think, and remember.

General Divisions of the Nervous System (Fritz 100-101)

• Central Nervous System (CNS): Consists of the brain, spinal cord, and their coverings. It is termed "central" because it integrates information from the entire body and coordinates activity across the organism.

• Peripheral Nervous System (PNS): Consists of the cranial nerves, spinal nerves, and ganglia (nerve bundles). Its primary function is to connect the CNS to the limbs and organs, serving as a relay between the brain/spinal cord and the rest of the body.

Divisions of the Peripheral Nervous System (PNS)

• Somatic Nervous System (SNS): A voluntary system that keeps the body in balance with the external environment.

  • It transmits impulses between the CNS and skeletal muscles, joints, bones, and skin.

  • It carries motor impulses to skeletal muscles and receives sensory input (pain, tension, stretching, temperature) from receptors.

• Autonomic Nervous System (ANS): An involuntary system that functions without conscious participation.

  • It controls visceral functions by sending impulses to smooth muscle, the heart, and glands.

  • Regulated functions include heart rate, blood vessel contraction/dilation, smooth muscle activity, visual accommodation, pupil size, and gland secretion.

Divisions of the Autonomic Nervous System (ANS)

• Sympathetic Autonomic Nervous System (SANS): Known as the "Fight or Flight" system.

  • Dominance: Active during stress (anger, fear, anxiety, excitement) and physical activities of certain intensities.

  • Function: Mobilizes the body for action and prepares it for stress.

  • Location: Nerves are found in the thoracolumbar area of the spinal cord.

• Parasympathetic Autonomic Nervous System (PANS): Known as the "Rest and Digest" system.

  • Dominance: Active during calm, non-stressful conditions, rest, and repair.

  • Function: Stimulates digestion and elimination; slows the heart rate; prepares the body for rest.

  • Location: Nerves are found in the craniosacral region of the spinal cord.

Comparative Functions of the ANS

Anatomy and Physiology of the Brain (Fritz 112-121)

• General Characteristics: The brain is the largest and most complex unit of the nervous system, containing approximately $100 \times 10^{9}$ ($100$ billion) neurons packed inside the skull.

• Main Areas of the Brain:

  • Cerebrum (Forebrain): The largest and most important portion.

    • Function: Receives sensory information, interprets it, relates it to past memories, and sends a corresponding motor response.

    • Cerebral Cortex: The outer layer controlling conscious behavior, memory, attention, perception, language, thought, and voluntary movement.

    • Hemispheres: Divided into Left (controls right side of body) and Right (controls left side of body).

    • Corpus Callosum: Nervous tissue connecting the two hemispheres, allowing them to work together.

    • Lobes:

      • Frontal: Motor center, language, and personality.

      • Parietal: Sensory center (taste, touch, pain), interpretation of language, and reading.

      • Temporal: Auditory and smell center.

      • Occipital: Vision center.

      • Insula (Island of Reil): The fifth lobe, located within the limbic system.

  • Cerebellum: Located inferior to the occipital lobes. Second-largest part of the brain. Responsible for coordination, muscle tone regulation, posture, and balance. Its functions are involuntary.

  • Brainstem: Formed by the Midbrain, Pons, and Medulla Oblongata.

    • Midbrain: Extends from pons to hypothalamus. Responsible for visual and auditory reflexes (e.g., ducking when a bee flies at you) and balance.

    • Pons (Bridge of Varolius): Located in the upper part of the medulla. Contains centers for breathing, eye movement, and facial expression.

    • Medulla Oblongata: Extends from spinal cord to pons. Connects brain and spinal cord. Regulates "Vital Signs" (heart rate, blood pressure, breathing) and reflexes like coughing, sneezing, swallowing, and vomiting.

  • Diencephalon: Located between the cerebrum and midbrain.

    • Thalamus: Relay station for all sensory input except smell. Associated with pain, temperature, and muscle reflex coordination. Relays pleasant/unpleasant feelings to the limbic system.

    • Hypothalamus: Located below the thalamus and above the pituitary. Acts as the "body thermostat" and a great regulator of homeostasis.

      • Functions: Coordinates ANS (sympathetic/parasympathetic), heart rate, blood pressure, digestion, appetite, satiety, sleep cycles, and water balance.

      • Mind/Body Link: Connects the nervous and endocrine systems, allowing the mind to affect the body.

Specialized Brain Structures

• Basal Ganglia: Deep islands of gray matter responsible for automatic voluntary movements and postures. Dysfunction is linked to disorders like Parkinson's disease.

• Limbic System: Related to emotions, smell, memory (long/short term), and feelings. Known as the "center of pleasure."

  • Endorphins: Secreted in this area, causing an analgesic effect (reducing pain and negative stress effects).

Urinary System (Fritz 633-637)

• Definition: Often viewed as only urine production, it is technically a "blood plasma balancer." It regulates water content, ion levels (sodium, potassium), and pH to maintain homeostasis.

• pH: Potential of Hydrogen. Used to determine acid/base content. The kidneys ultimately regulate the body's pH.

• Divisions:

  • Upper Tract: Including $2$ kidneys and $2$ ureters.

  • Lower Tract: Including $1$ urinary bladder and $1$ urethra.

Anatomy and Physiology of the Kidneys

• Location: Bean-shaped glands located at the back of the abdominal cavity from $T12$ to $L3$. The right kidney is lower due to the liver. Reference point: $12$th rib.

• Essential Functions:

  • Filtering blood plasma and excreting urine.

  • Controlling blood volume (plasma and red blood cells).

  • Regulating electrolyte levels (Sodium, Potassium, Calcium, Magnesium, Chloride, Phosphate, Sulfate, Bicarbonate).

  • Maintaining acid-base balance and tissue fluid levels.

  • Renin Production: A hormone that contracts blood vessels to raise blood pressure when it is low.

• Internal Anatomy:

  • Renal Cortex: Outer portion.

  • Renal Medulla: Innermost part.

  • Renal Pyramids: Triangular tissue masses in the medulla.

  • Renal Pelvis: Cavity at the beginning of the ureter; a common collector for calyces.

  • Calyces: Cup-shaped structures (major and minor) that lead into the renal pelvis.

  • Hilum: The entry/exit point for the renal artery, vein, and ureter.

The Nephron: Functional Unit of the Kidney

• Quantity: Millions per kidney.

• Three Processes of Urine Formation:

  1. Filtration: Movement of water and solutes from plasma.

  2. Reabsorption: Movement of molecules from the tubule back into the blood.

  3. Secretion: Movement of molecules from the blood into the tubule for excretion.

• Nephron Anatomy:

  • Renal Corpuscle: Includes the Glomerulus (capillary network for plasma filtration) and Bowman's Capsule (cup-shaped origin of the nephron).

  • Afferent Arteriole: Moves blood into the kidney.

  • Efferent Arteriole: Moves blood out of the kidney.

  • Renal Tubule: Includes the Proximal Tubule (closest to capsule), Henle's Loop (in the medulla), and Distal Tubule (connects to collecting tube).

  • Collecting Duct: Straight duct formed by many distal tubules; joins others in the renal pyramid.

Path of Urine and Blood Flow

• Urine Path: Proximal tubule $\rightarrow$ Henle's loop $\rightarrow$ Distal tubule $\rightarrow$ Collecting duct $\rightarrow$ Pyramid $\rightarrow$ Calyces $\rightarrow$ Renal pelvis $\rightarrow$ Ureter.

• Blood Flow Sequence: Abdominal aortic artery $\rightarrow$ renal artery $\rightarrow$ segmental arteries $\rightarrow$ lobar arteries $\rightarrow$ interlobular artery $\rightarrow$ arcuate artery $\rightarrow$ afferent arteriole $\rightarrow$ glomerulus $\rightarrow$ efferent arteriole $\rightarrow$ peritubular capillaries $\rightarrow$ venules $\rightarrow$ interlobular veins $\rightarrow$ arcuate veins $\rightarrow$ segmental veins $\rightarrow$ renal vein $\rightarrow$ inferior vena cava.

Lower Urinary Tract

• Ureters: Two ducts pushing urine from kidneys to bladder via peristalsis. They lie within the psoas muscle.

• Bladder: Hollow organ made of elastic fibers and smooth tissue (detrusor muscle). Stores urine. Located behind the symphysis pubis and in front of the rectum.

  • Capacity: Can hold up to $800\,ml$; the sacral region detects changes between $200 - 400\,ml$.

• Urethra: Extends from bladder to body exterior.

  • Dimensions: Women's measures approximately $1$ to $1.5$ inches; men's measures $7$ to $8$ inches.

  • Male Specifics: The male urethra is part of both the urinary and reproductive systems (ejaculatory ducts empty into it).

Urine Characteristics and Urination

• Composition: $95\%$ water, $5\%$ nitrogenous waste (urea, uric acid, ammonia, creatinine), electrolytes, toxins, pigments (from red blood cell breakdown), and hormones.

• Hormonal Influence: Antidiuretic Hormone (ADH) stimulates water retention by the kidneys.

• Urination (Micturition): Triggered by a spinal cord reflex. Pelvic muscles contract to hold urine and relax to eliminate it; the bladder relaxes to store and contracts to eliminate.

• Kegel Exercises: Developed by Dr. Arnold Kegel in the 1940s to strengthen pelvic muscles and control incontinence.

Disorders and Conditions

• Urinary Disorders:

  • Cystitis: Bladder inflammation (more common in women due to shorter urethra).

  • Nephritis: Inflammation of nephrons.

  • Pyelonephritis: Kidney inflammation from a UTI traveling from the urethra/bladder. Symptoms: fever, frequent urination, back/side/groin pain.

  • Glomerulonephritis: Injury to the glomeruli filtration system.

  • Urolithiasis (Kidney Stones): Crystalline substances (calcium, amino acids, etc.). Main cause is dehydration.

• Reproductive/Associated Disorders:

  • Dyspareunia: Painful sexual intercourse.

  • Toxic Shock Syndrome: Life-threatening bacterial toxins (Staphylococcus aureus), associated with high-absorbency tampons.

  • Bartholin's Cysts: Obstructed gland opening in females.

  • Myoma: Benign tumor in the myometrium.

  • Endometriosis: Endometrial tissue outside the uterus (ovaries, tubes, etc.); common in women $25 - 50$ who haven't had children.

  • Inflammations: Metritis (uterus), Endometritis (endometrium), Cervicitis (cervix).

Control Questions & Discussion

• Question: What structure of the male reproductive system is also part of the urinary system?

  • Answer: B. The urethra.

• Question: The urine passes from the kidneys to the bladder through:

  • Answer: A. Ureter.

• Question: Increases in calcium in the blood can cause the formation of stones in the kidneys. This condition is called:

  • Answer: C. Urolithiasis.

• Question: What is the function of the ureters?

  • Answer: Transport urine from the kidney to the bladder.

• Question: The scrotum is best described as:

  • Answer: B. A pouch of skin containing the testicles.

• Question: The condition in which the testicles fail to descend to the scrotum is called:

  • Answer: C. Cryptorchidism.

• Question: The tissue layer that lines the inside of the uterus is called:

  • Answer: B. Endometrium.

• Question: The gland that is at the base of the bladder and produces a milky fluid that empties into the urethra is known as:

  • Answer: [Context cutoff, likely the Prostate].