A & P Exam 2

Endocrine System

• Definition: A system of ductless glands that release hormones into the bloodstream to regulate long-term body processes such as growth, metabolism, reproduction, and homeostasis.

Glands

• Definition: Organs that produce and secrete substances.

  • Endocrine Glands: Secrete hormones directly into the blood.

  • Exocrine Glands: Secrete substances into ducts (e.g., sweat, saliva).

Hormones

• Definition: Chemical messengers released into the blood that bind to specific receptors on target cells.

Target Cells

• Definition: Cells that have specific receptors for a hormone and respond when that hormone binds.

Portal System

• Definition: A specialized blood vessel system connecting two capillary beds directly.

  • Example: Hypothalamo-hypophyseal portal system.

Endocrine vs. Nervous System

• Comparison Table:

  • Feature | Endocrine System | Nervous System

  • Signal Type | Hormones (chemical) | Neurotransmitters (electrical + chemical)

  • Speed | Slower | Fast

  • Duration | Long-lasting | Short-lived

  • Specificity | Any cell with receptor | Specific synapse

• Similarities: Both regulate body functions and maintain homeostasis.

Up- & Down-Regulation (Clinically Important)

• Up-Regulation: Increase in the number of receptors → stronger response.

• Down-Regulation: Decrease in receptors → weaker response.

  • Clinical Importance:

    • Explains hormone resistance (e.g., insulin resistance in diabetes).

    • Affects medication effectiveness.

Hypothalamo-Hypophyseal Pathways

1. Hypothalamo-Hypophyseal Tract:

   • Type: Neural connection.

   • Pathway: Hypothalamus → posterior pituitary.

     • Releases: Antidiuretic Hormone (ADH) & Oxytocin.

2. Hypothalamo-Hypophyseal Portal System:

   • Type: Blood vessel connection.

   • Pathway: Hypothalamus → anterior pituitary.

     • Releases: Regulatory hormones.

Endocrine vs. Exocrine Glands

Functions of the Endocrine System

• Regulates metabolism.

• Controls growth & development.

• Maintains fluid/electrolyte balance.

• Controls reproduction.

• Maintains homeostasis.

• Manages stress response.

Endocrine Organ vs. Endocrine Tissue

• Endocrine Organ:

  • Definition: Primary function is hormone secretion.

  • Example: Thyroid gland.

• Endocrine Tissue:

  • Definition: Contains hormone-secreting cells within another organ.

  • Example: Pancreatic islets.

Major Endocrine Glands & Locations

• Hypothalamus: Location of neurosecretory cells (median eminence, infundibular stem, etc.).

• Pituitary Gland: Located in the sella turcica; connected by infundibulum, known as the "master gland".

• Thyroid Gland: Located in the anterior neck; regulates metabolism.

• Adrenal Glands: Located on top of kidneys; comprised of cortex & medulla.

• Pancreas: Located posterior to stomach; islets secrete insulin & glucagon.

Three Types of Regulation of Hormone Release

1. Hormonal Regulation:

   • Definition: One hormone stimulates another.

   • Example: Thyroid Stimulating Hormone (TSH) stimulates thyroid hormone release.

2. Humoral Regulation:

   • Definition: Blood levels trigger release.

   • Example: High glucose levels stimulate insulin release.

3. Neural Regulation:

   • Definition: Nerve stimulation.

   • Example: Sympathetic stimulation causes adrenal medulla activation.

Three Types of Hormones

First vs. Second Messenger

• First Messenger: The hormone that acts outside the cell.

• Second Messenger: An intracellular signal (e.g., cyclic AMP - cAMP).

  • Water-soluble hormones utilize second messenger systems.

Receptors & Cellular Response

• Principle: More receptors result in a stronger response; fewer receptors result in a weaker response.

• Response Intensity: Determined by hormone concentration and receptor number.

Structure of Endocrine Glands

• Common Features:

  • Highly vascular to facilitate blood flow.

  • Secretory cells arranged in cords or clusters.

  • No ducts present.

  • Surrounded by connective tissue capsule.

Hypothalamus–Pituitary Interaction

• Regulation:

  • The hypothalamus controls both anterior and posterior pituitary glands.

  • Anterior pituitary regulation is through the portal system.

  • Posterior pituitary is controlled via neural tracts.

  • Involves releasing and inhibiting hormones.

Hormone Pathways & Feedback

• Prolactin:

  • Pathway: Hypothalamus → inhibits via dopamine.

  • Type: Negative feedback.

• Growth Hormone (GH):

  • Pathway: GHRH → GH → Insulin-like Growth Factors (IGFs).

  • Type: Negative feedback.

• Luteinizing Hormone (LH) & Follicle Stimulating Hormone (FSH):

  • Pathway: GnRH → LH/FSH → Gonads.

  • Type: Negative feedback (regulated by estrogen/testosterone levels).

• Thyroid Hormone:

  • Pathway: TRH → TSH → T3/T4.

  • Type: Negative feedback.

• Cortisol:

  • Pathway: CRH → ACTH → Cortisol.

  • Type: Negative feedback.

• Insulin:

  • Trigger: High glucose levels → Insulin release.

  • Type: Humoral regulation.

• Glucagon:

  • Trigger: Low glucose levels → Glucagon release.

  • Type: Humoral regulation.

Oxytocin & ADH (Special Features)

• Oxytocin:

  • Function: Positive feedback mechanism, stimulates uterine contractions and milk let-down reflex.

• Antidiuretic Hormone (ADH):

  • Function: Regulates water balance; increases water reabsorption in the kidneys; controlled by osmolarity levels.

Cardiovascular System Study Guide

Key Definitions (Know & Apply)

• Autorhythmic: Ability of cardiac cells (specifically the SA node) to spontaneously generate action potentials without nervous input.

• Vagal Tone: The baseline parasympathetic influence from the vagus nerve that slows resting heart rate.

• Systole: The contraction phase of the heart, during which the ventricles eject blood.

• Diastole: The relaxation phase of the heart when ventricles fill with blood.

• Cardiac Output (CO): The amount of blood pumped by the heart per minute. Calculated as: CO = HR imes SV where HR = Heart Rate and SV = Stroke Volume.

• Heart Rate (HR): The number of beats per minute.

• Stroke Volume (SV): The amount of blood ejected with each beat.

• Venous Return: The amount of blood returning to the heart.

• Preload: The stretch of the ventricles before contraction, related to venous return.

• Frank-Starling Law: The principle stating that greater stretch leads to stronger contraction and increased stroke volume.

• Afterload: The resistance that ventricles must overcome to eject blood.

• Inotropic Agents: Substances that affect the strength of muscle contractions.

• Chronotropic Agents: Substances that affect heart rate.

Location & Characteristics of the Heart

• The heart is located in the mediastinum, between the lungs, and is posterior to the sternum, with the apex pointing left and the base facing posteriorly.

Blood Flow Through the Heart

1. Body → Superior/Inferior Vena Cava

2. Right Atrium

3. Tricuspid Valve

4. Right Ventricle

5. Pulmonary Valve

6. Pulmonary Trunk/Arteries

7. Lungs

8. Pulmonary Veins

9. Left Atrium

10. Mitral (Bicuspid) Valve

11. Left Ventricle

12. Aortic Valve

13. Aorta → Body

Why Left Ventricular Wall is Thicker

• It pumps blood to the entire body (systemic circulation) requiring higher pressure, while the right ventricle only pumps to the lungs (a low-pressure system).

Pulmonary vs. Systemic Circulation

• Unique Feature of Pulmonary Circulation: The pulmonary arteries carry deoxygenated blood.

Coronary Circulation

• The heart requires a continuous supply of oxygen, supplied mainly by the right and left coronary arteries, predominantly during diastole.

Cardiac Conduction System

• Components:

  • SA Node

  • AV Node

  • AV Bundle (Bundle of His)

  • Bundle Branches

  • Purkinje Fibers

• Function: Coordinates atrial and then ventricular contraction.

Layers of the Heart (Superficial → Deep)

1. Fibrous Pericardium

2. Parietal Serous Pericardium

3. Pericardial Cavity

4. Visceral Serous Pericardium (Epicardium)

5. Myocardium

6. Endocardium

Chambers & Valves

Cardiovascular System Functions

• Transport: Oxygen

• Remove: Carbon Dioxide

• Deliver: Nutrients

• Remove: Wastes

• Regulate: Temperature

• Maintain: pH

Baroreceptors & Chemoreceptors

• Baroreceptors: Detect blood pressure changes (located in carotid sinus, aortic arch).

• Chemoreceptors: Detect CO₂, O₂, pH levels.

• Responses:

  • Low BP → Increase HR & contractility.

  • High CO₂ → Increase HR & breathing rate.

Cardiac Centers in the Brain

• Located in the medulla oblongata:

  • Cardioacceleratory Center

  • Cardioinhibitory Center

Cardiac Muscle vs. Skeletal Muscle

EKG Components

• P wave: Atrial depolarization.

• QRS complex: Ventricular depolarization.

• T wave: Ventricular repolarization.

• PR interval: Time between P wave and QRS complex.

• QT interval: Time from the beginning of the Q wave to the end of the T wave.

Cardiac Cycle Steps

1. Ventricular Filling

2. Isovolumetric Contraction

3. Ventricular Ejection

4. Isovolumetric Relaxation

Factors Affecting Stroke Volume

1. Preload ↑ → SV ↑

2. Contractility ↑ → SV ↑

3. Afterload ↑ → SV ↓

Factors Affecting Heart Rate

• Sympathetic Stimulation: Increases HR.

• Parasympathetic Stimulation: Decreases HR.

• Hormones (Epinephrine): Increase HR.

• Temperature: Increase HR.

Blood Vessels Study Guide

Key Definitions (Know & Apply)

• Arteries: Carry blood away from the heart (usually oxygenated except for pulmonary arteries).

• Veins: Carry blood toward the heart (usually deoxygenated except for pulmonary veins).

• Capillaries: Microscopic vessels where exchange of gases, nutrients, and wastes occurs.

• Lumen: Open interior space of a vessel.

• Blood Pressure (BP): Force exerted by blood on vessel walls.

  • Systolic: Pressure during ventricular contraction.

  • Diastolic: Pressure during relaxation.

  • Pulse Pressure (PP): PP = Systolic − Diastolic.

  • Mean Arterial Pressure (MAP): MAP = Diastolic + (1/3) × Pulse Pressure.

• Blood Pressure Gradient: Blood flows from high pressure to low pressure.

• Resistance: Opposition to blood flow, influenced by vessel diameter (most important), blood viscosity, and vessel length.

• Skeletal Muscle Pump: Muscle contractions compress veins, aiding in blood return to the heart.

Why Capillaries Are Exchange Vessels

• Only one endothelial cell layer thick.

• Extremely thin walls facilitate exchange.

• Large surface area enhances diffusion.

• Slow blood flow allows time for exchange.

Why Veins Need Valves

• They operate as a low-pressure system.

• Blood must return against gravity, particularly from the lower limbs.

• Valves prevent backflow and ensure unidirectional flow toward the heart.

Hydrostatic & Osmotic Forces

• Hydrostatic Pressure: The blood pressure pushing fluid OUT of capillaries (filtration).

• Colloid Osmotic Pressure: The protein-based pressure pulling fluid INTO capillaries (reabsorption).

• Balance: Determines fluid movement into/out of capillaries.

Layers of Blood Vessels

• Common Layers (excluding capillaries):

  1. Tunica Intima: Endothelium providing a smooth surface.

  2. Tunica Media: Smooth muscle controlling vasoconstriction/dilation; thickest in arteries.

  3. Tunica Externa: Connective tissue providing protection and anchoring.

Artery vs. Vein Differences

Types of Arteries

• Elastic Arteries: Largest, proximal to the heart, stretch & recoil (e.g., Aorta).

• Muscular Arteries: Distribute blood to organs and have thick smooth muscles.

• Arterioles: Smallest arteries, major resistance vessels controlling blood flow into capillaries.

Types of Capillaries

Types of Veins

• Venules: Smallest veins that drain capillaries.

• Medium Veins: Contain valves.

• Large Veins: E.g., Vena cava with a large lumen.

Order of Blood Flow

• Heart → Elastic arteries → Muscular arteries → Arterioles → Capillaries → Venules → Veins → Heart

Types of Blood Flow Pathways

• Simple Pathway: Artery → Capillary → Vein.

• Portal System: Two capillary beds connected by a portal vein (Example: Hepatic portal system).

• Arteriovenous Anastomosis: Direct artery-to-vein connection (thermoregulation).

Capillary Exchange Methods

1. Diffusion

2. Filtration

3. Reabsorption

4. Transcytosis

Blood Pressure Regulation — Nervous System

• Brain Centers: Located in the medulla oblongata:

  • Cardioacceleratory center

  • Cardioinhibitory center

  • Vasomotor center

• Baroreceptors: Located in the carotid sinus and aortic arch to detect stretch (BP changes).

  • Responses:

    • Low BP → Increased HR & vasoconstriction.

    • High BP → Decreased HR & vasodilation.

Blood Pressure Regulation — Endocrine System

Systemic Vessels — General Info

• Initially a high-pressure system that decreases as vessels branch.

• Veins act as blood reservoirs.

Major Arteries of Systemic Circuit

• List:

  • Subclavian

  • Brachiocephalic

  • Brachial

  • Carotid

  • Aorta

  • Renal

  • Ulnar

  • Radial

  • Superior mesenteric

  • Inferior mesenteric

  • Common iliac

    • Internal iliac

    • External iliac

  • Femoral

  • Popliteal

  • Anterior tibial

  • Posterior tibial

  • Peroneal

Major Veins of Systemic Circuit

• List:

  • Superior vena cava

  • Inferior vena cava

  • Jugular veins

  • Subclavian veins

  • Hepatic portal vein

  • Iliac veins