Exam 1

🧠 ENDOCRINE SYSTEM

What Is the Endocrine System?

The endocrine system is a system of ductless glands that secrete hormones into the bloodstream to regulate body functions.

It controls:

  • Growth & development

  • Metabolism

  • Reproduction

  • Blood pressure

  • Stress response

  • Fluid & electrolyte balance

  • Circadian rhythms

Hormones = chemical messengers carried in blood.

Nervous vs Endocrine System

Feature

Nervous

Endocrine

Signal Type

Electrical + neurotransmitters

Hormones (chemical)

Speed

Very fast (milliseconds)

Slower (seconds–days)

Duration

Short-lived

Long-lasting

Specificity

Very targeted

Broader (cells with receptors)

Nervous = immediate response
Endocrine = long-term regulation

Exocrine vs Endocrine Glands

Exocrine

Endocrine

Have ducts

Ductless

Secrete onto surfaces

Secrete into blood

Example: sweat glands

Example: thyroid

Major Endocrine Organs (Location + Function)
Hypothalamus
Pituitary Gland

  • Sits in sella turcica of sphenoid bone

  • Anterior lobe (glandular tissue)

  • Posterior lobe (neural tissue)

Anterior hormones:

  • GH

  • TSH

  • ACTH

  • FSH

  • LH

  • Prolactin

Posterior stores/releases:

  • ADH

  • Oxytocin

Thyroid Gland

  • Anterior neck

  • Follicles filled with colloid

  • Hormones:

    • T3

    • T4

    • Calcitonin

Parathyroid

  • Posterior thyroid

  • Secretes PTH (raises blood calcium)

Adrenal Glands

  • On top of kidneys

Cortex (3 layers):

  • Zona glomerulosa → aldosterone

  • Zona fasciculata → cortisol

  • Zona reticularis → androgens

Medulla:

  • Epinephrine

  • Norepinephrine

Pancreas (Islets of Langerhans)

  • Alpha → glucagon

  • Beta → insulin

  • Delta → somatostatin

Why the Hypothalamus Is Unique

It links nervous system to endocrine system.
It receives neural input and converts it into hormonal output.

Chemical Messengers

  • Hormones

  • Neurotransmitters

  • Paracrines

  • Autocrines

Two Classes of Hormones
1. Lipid-Soluble (Steroid & Thyroid)

  • Derived from cholesterol

  • Cross membrane

  • Bind intracellular receptors

  • Affect gene transcription

  • Slow but long lasting

2. Water-Soluble (Peptide & Amine)

  • Bind membrane receptors

  • Use second messenger systems

  • Fast but short-lived

Hormone Mechanism of Action (MOA)

Water-soluble:

  1. Hormone binds membrane receptor

  2. Activates G-protein

  3. Activates adenylate cyclase

  4. Converts ATP → cAMP

  5. cAMP activates protein kinase

  6. Cellular response

This is the second messenger system.

Hormone Effects on Target Cells

A cell must have:

  • Specific receptor

  • Proper signaling pathway

Effects depend on:

  • Receptor number

  • Hormone concentration

  • Affinity

Hormone Interactions

Permissiveness → one hormone enhances another
Synergism → combined effect greater than sum
Antagonism → opposite effects

Example:

  • Insulin vs glucagon = antagonistic

Endocrine Gland Stimuli

  1. Hormonal stimulus (TSH → thyroid)

  2. Humoral stimulus (blood calcium → PTH)

  3. Neural stimulus (sympathetic → adrenal medulla)

🩸 BLOOD

Major Functions of Blood

  • Transport gases

  • Transport nutrients

  • Waste removal

  • Hormone transport

  • Immune defense

  • Clotting

  • pH regulation

  • Temperature regulation

Blood Is a Connective Tissue

  • Matrix = plasma

  • Cells = formed elements

  • It is a suspension (cells suspended in liquid)

Composition

  • 55% Plasma

  • 45% Formed elements

Hematocrit

Percentage of blood volume made of RBCs.

Most Abundant Plasma Protein

Albumin (maintains osmotic pressure)

Physical Characteristics

  • Slightly alkaline (7.35–7.45)

  • 5–6 liters

  • Sticky, viscous

  • Red color from hemoglobin

Formed Elements
Erythrocytes (RBCs)

  • Transport oxygen

  • No nucleus

  • Contain hemoglobin

Leukocytes (WBCs)

Granulocytes:

  • Neutrophils

  • Eosinophils

  • Basophils

Agranulocytes:

  • Lymphocytes

  • Monocytes

Platelets

  • Cell fragments

  • Clot formation

Hemoglobin

Protein responsible for gas transport
Contains iron

Forms:

  • Oxyhemoglobin (with oxygen)

  • Deoxyhemoglobin (without oxygen)

  • Carbaminohemoglobin (with CO₂)

Erythropoiesis (RBC Formation)

  1. Hemocytoblast (stem cell)

  2. Proerythroblast

  3. Erythroblast

  4. Normoblast

  5. Reticulocyte

  6. Mature RBC

Stimulated by erythropoietin (kidneys)

Leukopoiesis (WBC Formation)

Same stem cell → myeloid or lymphoid lineages.

Hemostasis (Stopping Bleeding)

3 Steps:

  1. Vascular spasm

  2. Platelet plug formation

  3. Coagulation (fibrin clot)

Hemostasis Disorders

  • Hemophilia

  • Thrombocytopenia

  • Thrombus

  • Embolus

Blood Typing

ABO System:

  • Type A

  • Type B

  • Type AB

  • Type O

Rh factor (+ or -)

Transfusion compatibility depends on antigens & antibodies.

❤ HEART & CIRCULATION

Location & Coverings

Located in mediastinum.

Layers:

  • Fibrous pericardium

  • Serous pericardium

  • Epicardium

  • Myocardium

  • Endocardium

Circuits of the Heart
Pulmonary Circuit

Right heart → lungs → left heart

Systemic Circuit

Left heart → body → right heart

Blood Flow Pathway

SVC/IVC → Right atrium → Tricuspid valve → Right ventricle → Pulmonary valve → Lungs → Left atrium → Mitral valve → Left ventricle → Aortic valve → Aorta

Cardiac cycle ≈ 0.8 seconds

Heart Valves

AV valves:

  • Tricuspid

  • Mitral

Semilunar valves:

  • Pulmonary

  • Aortic

Open/close due to pressure changes.

Electrical Conduction System

  1. SA node (pacemaker)

  2. AV node

  3. Bundle of His

  4. Bundle branches

  5. Purkinje fibers

EKG Correlation

P wave → atrial depolarization
QRS → ventricular depolarization
T wave → ventricular repolarization

Mechanical Events

  • Atrial systole

  • Ventricular systole

  • Diastole

Extrinsic Heart Rate Control

Sympathetic → increases HR
Parasympathetic (vagus nerve) → decreases HR

Regulation of Pumping

Cardiac output = HR × stroke volume

Affected by:

  • Preload

  • Afterload

  • Contractility

  • Venous return