Human Physiology: Essential Mechanisms and Functions

Posted on Dec 16, 2024 in Biology

Blood Glucose Regulation

Rising blood glucose – Detected by insulin-secreting cells in the pancreas. The pancreas secretes insulin, causing body and liver cells to take up glucose and store it as glycogen. Glucose levels decline, and insulin release stops. Return to homeostatic blood glucose level.

Specialization of Cardiac Muscle Cells

Describe the specialization of cardiac muscle cells and how they support the electrical and mechanical functions of the heart:

  • Intercalated Discs: Specialized connections in heart cells with gap junctions for rapid electrical signal transmission and desmosomes for mechanical strength, ensuring synchronized contraction and preventing cell separation.
  • Striations: Cardiac muscle cells, like skeletal muscle, have a regular arrangement of actin and myosin filaments, allowing for efficient contraction.
  • Branching: Cardiomyocytes are branched, aiding in the distribution of electrical impulses and mechanical force throughout the heart muscle.

Electrical Function

  • Synchrony: Gap junctions ensure quick, uniform electrical impulses for coordinated heartbeats.
  • Automaticity: Pacemaker cells generate and propagate impulses without external stimuli.

Mechanical Function

  • Durability: Desmosomes and structural integrity withstand heartbeat stress.
  • Efficiency: Striations and organized filaments enable powerful, efficient contractions.

These ensure the heart functions efficiently, maintaining rhythmic contractions and enduring workload.

Effects of Blood Donation

Adult female donates blood:

Short-Term Effects

  • Vasoconstriction: Of blood vessels to maintain blood pressure.
  • Increased Heart Rate: Faster to compensate for less blood volume.
  • Hormone Release: Adrenaline and noradrenaline help vasoconstriction and heart rate.
  • Fluid Shift: To the bloodstream to increase volume.

Long-Term Responses

  • Increased production of new red blood cells.
  • Kidneys retain more fluid and sodium.
  • Plasma Volume Restoration.
  • The cardiovascular system adapts to the new blood volume.

These mechanisms ensure the body maintains optimal blood pressure.

Electrocardiogram (ECG)

  • P Wave: Atrial depolarization → Atrial contraction.
  • QRS Complex: Ventricular depolarization → Ventricular contraction.
  • T Wave: Ventricular repolarization → Ventricular relaxation.

Oxygen and Carbon Dioxide Transport in Blood

How is O2 and CO2 transported in blood:

O2 Transport

Most oxygen binds to hemoglobin molecules in red blood cells, forming oxyhemoglobin. A small amount is dissolved directly in the blood plasma.

CO2 Transport

  • About 70% of CO2 is transported as bicarbonate ions in the plasma, formed through a reaction with water.
  • Carbaminohemoglobin: Around 20% binds to hemoglobin in red blood cells.
  • About 10% is dissolved directly in the blood plasma.

Ventilation-Perfusion Matching

Ventilation-perfusion matching ensures efficient gas exchange in the alveoli:

  • Ventilation: Brings oxygen into the alveoli.
  • Perfusion: Blood brings CO2 to be exchanged for O2.
  • Regulation:
    • Vasodilation/Vasoconstriction: Adjusts blood flow to match ventilation.
    • Bronchodilation/Bronchoconstriction: Adjusts airflow to match blood flow.

These mechanisms optimize gas exchange by matching airflow with blood flow.

Glomerular Filtration Rate (GFR) Regulation

Glomerular filtration rate Regulation Mechanisms:

Autoregulation

  • Myogenic Mechanism: Afferent arterioles constrict/dilate in response to blood pressure changes to maintain GFR.
  • Tubuloglomerular Feedback: Macula densa cells detect NaCl levels, adjusting arteriole size to regulate GFR.

Hormonal & Neural Mechanisms

  • Renin-Angiotensin-Aldosterone System (RAAS): Low blood pressure triggers renin release, leading to angiotensin II production, vasoconstriction, and increased GFR.
  • Sympathetic Nervous System: Acute stress causes arteriole constriction to preserve blood volume and pressure.
  • Prostaglandins: Help counteract excessive vasoconstriction, ensuring adequate blood flow to the glomerulus.

These mechanisms keep GFR stable despite blood pressure fluctuations.

Glomerular Filter Features

Glomerular Filter Features:

  • Fenestrated Endothelium: Allows small molecules to pass, blocking larger proteins and cells.
  • Glomerular Basement Membrane: Acts as a barrier, restricting larger molecules and negatively charged substances.
  • Podocytes: Create filtration slits for size-selective filtration.

Support for Filtration

  • Selective Permeability: Ensures only small molecules pass into the Bowman’s capsule.
  • Efficient Filtration: Large surface area and high permeability enhance blood filtration.
  • Maintains Blood Components: Prevents loss of essential proteins and cells.

Absorption of Lipids vs. Proteins

Ways absorption of digested lipids differs from proteins:

  1. Lipids require emulsification and are transported via the lymphatic system, while proteins are directly absorbed into the bloodstream.
  2. Lipids are reassembled into triglycerides before transport, while proteins are directly absorbed as amino acids into the bloodstream.
  3. Lipids are absorbed into intestinal cells and reassembled into triglycerides, whereas proteins are absorbed directly into the bloodstream as amino acids.

Comparison with Starch

Lipids are emulsified, reassembled, and transported via the lymphatic system, whereas proteins and starches are absorbed directly into the bloodstream without emulsification. Proteins use active transport, while starches use active transport and facilitated diffusion.

Gastrointestinal Hormones

Gastrointestinal hormones sites:

  • Gastrin:
    • Site: Stomach.
    • Function: Stimulates gastric acid secretion.
  • Cholecystokinin:
    • Site: Small intestine.
    • Function: Promotes enzyme release from the pancreas and bile from the gallbladder.
  • Secretin:
    • Site: Small intestine.
    • Function: Stimulates bicarbonate secretion to neutralize stomach acid.

These hormones ensure efficient digestion and nutrient absorption.

Role of Elastic Arteries

What is the role of elastin in arteries:

Role of Elastic Arteries

  • Pressure Reservoirs: Maintain blood flow during diastole by recoiling after systole to maintain blood flow to organs even when the heart isn’t pumping.

Structural Features

  • Elastic Fibers: Allow stretching and recoiling.
  • Thick Walls: Withstand high pressure.
  • Smooth Muscle: Regulate diameter and maintain vessel integrity.

These help blood flow and help manage blood pressure.

Action Potentials and Cardiac Muscle Control

Describe how action potentials control cardiac muscle:

Excitation-Contraction Coupling in Cardiac Muscle Cells

  • Action Potential: Starts in the sinoatrial node and spreads through the heart.
  • Depolarization: Na+ ions enter the cell.
  • Calcium Influx: Ca2+ enters through L-type channels and releases more Ca2+ from the sarcoplasmic reticulum.
  • Contraction: Ca2+ binds to troponin, enabling actin-myosin interaction, leading to muscle contraction.
  • Relaxation: Ca2+ is removed from the cytoplasm, leading to muscle relaxation.

Key Processes

  • Contraction: Ca2+ binds to troponin, allowing actin-myosin interaction.
  • Relaxation: Ca2+ is pumped out, stopping the interaction, and relaxing the muscle.

Kidneys and Long-Term Blood Pressure Regulation

Kidneys’ long-term blood pressure regulation:

Through several mechanisms:

Renin-Angiotensin-Aldosterone System (RAAS)

  • Renin: Released by the kidneys in response to low blood pressure.
  • Angiotensin II: Causes vasoconstriction and stimulates aldosterone release, which increases blood volume and pressure.
  • Antidiuretic Hormone (ADH): Promotes water reabsorption.

Sodium and Water Balance

  • Direct Regulation: Adjusts sodium and water reabsorption to control blood volume and pressure.

Autonomic Nervous System

  • Sympathetic Nervous System: Increases renin release and sodium reabsorption, raising blood pressure.

Effects of Hydration on the Body

Hydrated person drinks 1.5L of water:

  • Water Intake: Increases blood volume and decreases plasma osmolarity.
  • ADH Reduction: Less ADH is secreted, reducing water reabsorption in the kidneys.
  • Distal Tubules: Cells become less water-permeable, increasing urine output.
  • Homeostasis: Plasma osmolarity and blood volume return to normal levels.

This ensures that the body effectively regulates its fluid balance after ingesting a large volume of water.

Mechanisms of Normal Breathing

Mechanisms of normal/quiet breathing:

  • Inspiration: Diaphragm and external intercostal muscles contract, intrapleural pressure decreases, lung volume increases, and alveolar pressure decreases, allowing air in.
  • Expiration: Diaphragm and external intercostal muscles relax, intrapleural pressure increases, lung volume decreases, and alveolar pressure increases, pushing air out.

Substances in Saliva and Their Control

Saliva contains water, mucus, amylase, lingual lipase, lysozyme, bicarbonate ions, electrolytes, and immunoglobulin A, each with specific functions in digestion, lubrication, and immune defense. The flow of saliva is mainly controlled by the autonomic nervous system, with parasympathetic stimulation increasing production and sympathetic stimulation producing less, thicker saliva.

Digestion and Absorption of Starch and Triglycerides

Digestion and absorption of starch/triglycerides:

Starch is broken down by amylases into glucose, which is directly absorbed into the bloodstream. Triglycerides (lipids) are emulsified by bile salts and digested by lipases into fatty acids and monoglycerides, which are reassembled and transported via chylomicrons through the lymphatic system. Bile aids in fat digestion and absorption.

Oxygen and Carbon Dioxide Exchange and Hemoglobin Affinity

Control of O2/CO2 exchange in tissue and lungs & affinity:

Exchange in the Tissues

  • O2 Release: O2 dissociates from hemoglobin to be used by tissues.
  • CO2 Uptake: CO2 produced by cellular respiration is converted into bicarbonate ions for transport.

Exchange in the Lungs

  • O2 Uptake: O2 diffuses into the blood from the alveoli, binding to hemoglobin.
  • CO2 Release: CO2 diffuses into the alveoli from the blood to be exhaled.

Factors Affecting Hemoglobin Affinity for O2

  • Partial Pressure of O2: Higher pressure increases affinity.
  • pH (Bohr Effect): Lower pH decreases affinity, enhancing O2 release.
  • Partial Pressure of CO2: Higher CO2 levels decrease affinity.
  • Temperature: Higher temperatures decrease affinity.
  • 2,3-Bisphosphoglycerate (2,3-BPG): Higher levels decrease affinity.

Substances Secreted into the Stomach During Digestion

Substances secreted into the stomach during digestion:

The stomach secretes hydrochloric acid for protein digestion, pepsinogen, mucus to protect the lining, intrinsic factor for vitamin B12 absorption, and gastrin to stimulate secretion. These processes are controlled by the vagus nerve, the enteric nervous system, gastrin to enhance secretion, and somatostatin to inhibit when pH is low. These mechanisms ensure effective digestion and an optimal enzyme environment.