Endocrine System and Cell Communication

CHAPTER II: Cell Communication

Outgoing Signal and Physiological Response

  • The process of outgoing signals in cells leads to physiological responses in other cells.

Signal Transduction

  • Definition: The conversion of an impulse or stimulus from one physical or chemical form to another.

  • Role of Intracellular Signaling Molecules: They alter cell behavior after a target cell converts an extracellular signal into an intracellular signal.

  • Mechanism: Signals bind to receptor proteins, initiating a physiological response.

General Principles of Cell Signaling

  1. Signal Range:

    • Signals can act over a long or short range.

  2. Variety in Responses:

    • A limited set of extracellular signals can produce a huge variety of cell behaviors.

  3. Response Speed:

    • A cell's response to a signal can be fast or slow.

Cell-Surface Receptors

  • Functions: Relay extracellular signals via intracellular signaling pathways.

  • Molecular Switches: Some intracellular signaling proteins act as molecular switches.

  • Signal Integration: Signals integrate to produce a physiological response.

Hormones and Local Signals

  • Hormones:

    • Travel long distances to other parts of the body (e.g., insulin, endocrine signaling).

  • Paracrine Signals:

    • Growth factors that travel short distances.

  • Importance: Long/short-range signaling is crucial in determining cell fates.

Glandular Functions

Exocrine Glands:

  • Definition: Secrete products through ducts onto epithelial surfaces (e.g., skin, digestive tract).

  • Functions: Extracellular effects such as digestion of food.

  • Example: Mixed glands include the liver and pancreas.

Endocrine Glands:

  • Definition: No ducts, high density of capillaries (fenestrated).

  • Functions: Secretions enter the bloodstream (internal secretions) and bind to target cells (also known as receptors), leading to intracellular effects that alter metabolism.

Development of Exocrine and Endocrine Glands

  • Exocrine + Endocrine Glands

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Neuroendocrine Cells

  • Definition: Hybrid cells that combine features of neurons and endocrine cells.

  • Function: They convert electrical signals into hormonal signals.

Endocrine System

  • Components: Glands, tissues, and cells that secrete hormones.

  • Endocrinology: The study of the endocrine system, including the diagnosis and treatment of its disorders.

  • Key Endocrine Glands:

    • DHEA (Dehydroepiandrosterone): Source is the adrenal cortex.

    • IGFs (Insulin-like Growth Factors or Somatomedins): Source is the liver and other tissues.

Pancreas

  • Both an endocrine and exocrine gland.

  • Structures: Islets of Langerhans, acinar cells, pancreatic ducts.

Hypothalamus and Pituitary Gland

  • Function:

    • Regulates hunger and thirst, connected to the hypothalamus.

    • No master control; involved in temperature homeostasis, sex drive, and two divisions related to pregnancy and childbirth.

  • Anterior Pituitary:

    • Key feature: Grows 50% during pregnancy, high range of control including stress response.

  • Posterior Pituitary:

    • Composed of nervous tissue, not a true gland.

    • Neuroendocrine cells of the hypothalamus produce hormones that travel to the posterior pituitary and are stored in nerve endings.

Hormones of Hypothalamus

  • Relationship to Anterior Pituitary: Hormones regulate the anterior pituitary and are stored in the posterior pituitary.

  • Total: 8 hormones (releasing and inhibiting hormones).

  • Examples:

    • Somatostatin: Growth hormone inhibitor.

    • Thyrotropin-Releasing Hormone (TRH): Stimulates thyroid hormone production.

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Anterior Pituitary Hormones

  1. Follicle-Stimulating Hormone (FSH):

    • Function: Stimulates development of ovarian follicles and sperm production.

    • Regulated by: Gonadotropin-Releasing Hormone (GnRH).

  2. Luteinizing Hormone (LH):

    • Target: Ovaries and testes.

    • Functions: Ovulation, corpus luteum formation, secretion of testosterone.

  3. Thyroid-Stimulating Hormone (TSH):

    • Target: Thyroid gland.

    • Function: Stimulates thyroid hormone secretion and growth.

  4. Adrenocorticotropic Hormone (ACTH):

    • Target: Adrenal cortex.

    • Function: Stimulates release of glucocorticoids and regulates metabolism.

  5. Prolactin (PRL):

    • Target: Mammary glands.

    • Function: Stimulates milk production.

  6. Growth Hormone (GH):

    • Target: Various tissues.

    • Functions: Stimulates growth and metabolism.

    • Regulated by: Growth Hormone-Releasing Hormone (GHRH).

Posterior Pituitary Hormones

  1. Antidiuretic Hormone (ADH):

    • Target: Kidneys.

    • Function: Concentrates urine and conserves water, prevents dehydration.

  2. Oxytocin (OT):

    • Target: Reproductive tissues and brain.

    • Function: Triggers contractions during childbirth and milk ejection, influences maternal bonding.

Examples of Hormonal Interaction

  • Anterior vs. Posterior Pituitary Response:

    • Stress and dehydration lead to specific releases of hormones (e.g., ACTH during stress, ADH for dehydration).

  • Blood-water concentration regulated through the hypothalamus and associated feedback loops.

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Control of Pituitary Glands

  • Hormones are not produced at constant rates.

  • Control Mechanisms:

    • Feedback from target organs.

    • Brain monitors conditions, stimulates or inhibits pituitary gland (e.g., stress/hypothalamus release CRH).

    • Neuroendocrine Reflexes that control the posterior pituitary gland are triggered by physiological changes (e.g., blood osmolarity).

Function of Blood Vessels in Posterior Pituitary

  • Purpose: To carry hormones (ADH + Oxytocin) from the posterior pituitary into the bloodstream and provide oxygen/nutrients to the nervous tissue.

Thyroid Gland

  • Only function is endocrine:

    • Monitored by brain for basal metabolic rate (BMR).

    • Controls BMR by releasing TRH from hypothalamus.

    • Structure: Contains thyroid follicles composed of follicular cells that secrete thyroid hormones (TH), and parafollicular cells that secrete calcitonin (regulates calcium levels).

Parathyroid Glands

  • Location: 4 glands located behind the thyroid gland.

  • Secretion: Parathyroid hormone (PTH) that regulates calcium levels in blood directly without pituitary influence.

  • Response: Stimulates osteoclasts to reabsorb calcium into the blood when levels are low.

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Adrenal Glands

  • Location: Situated atop the kidneys.

  • Components:

    • Adrenal Medulla: Produces catecholamines (e.g., epinephrine and norepinephrine) in response to stress.

    • Adrenal Cortex: Secretes steroid hormones, including glucocorticoids, mineralocorticoids, and sex hormones.

    • Functions of the Medulla and Cortex: Help in managing stress, regulating electrolytes, and maintaining metabolism.

Adrenal Medulla

  • Definition: Neuroendocrine tissue influenced by the sympathetic nervous system.

  • Secretion: Produces epinephrine and norepinephrine during fight or flight response.

Adrenal Cortex

  • Categories of Hormones Produced:

    1. Mineralocorticoids: Regulate electrolyte balance.

    2. Glucocorticoids: Regulate glucose metabolism (e.g., cortisol).

    3. Sex Steroids: Involved in reproductive functions.

Pancreas

  • Structure: Composed of islets of Langerhans (endocrine) and acinar cells (exocrine).

    • Alpha Cells (20%): Secrete glucagon to increase blood glucose levels between meals.

    • Beta Cells (70%): Secrete insulin to decrease blood glucose levels after meals.

    • Delta Cells (5%): Secrete somatostatin to limit gastric acid secretion.

Gonads

  • Function: Both endocrine and exocrine.

    • Ovaries: Produce estradiol and progesterone, regulating the menstrual cycle and sustaining pregnancy.

    • Testes: Produce testosterone, regulating development and sex drive.

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CHAPTER 12: Hormone Chemistry

Chemical Classes of Hormones

  1. Steroids:

    • Derived from cholesterol (e.g., sex steroids like progesterone and testosterone).

    • Corticosteroids such as cortisol.

  2. Monoamines:

    • Synthesized from amino acids (e.g., dopamine, epinephrine, norepinephrine, melatonin, TH).

  3. Peptides:

    • Chains of 3 to 200+ amino acids (e.g., releasing and inhibiting hormones from the hypothalamus, most pituitary hormones).

Hormone Synthesis

  • Steroids: Tailored by functional groups added to the cholesterol backbone.

  • Monoamines: Derive specific structures from tyrosine and tryptophan.

  • Peptides: Produced similarly to proteins (transcription, translation, folding, and modification).

Hormone Secretion

  • Hormones are secreted in a regulated manner influenced by various stimuli:

    • Neural Stimuli: Nerve fibers stimulate hormone release (e.g. epinephrine secretion).

    • Hormonal Stimuli: Tropic effects (e.g. TSH–TH regulation).

    • Humoral Stimuli: Influenced by blood-borne stimuli (pressure and substance levels).

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Function of Hormones in Gonads

  • Expected production of sex hormones (e.g., estrogen and testosterone).

  • Thyroid hormone production requires thyroglobulin and iodine.

  • Parathyroid hormone on PTH secretion is controlled by blood calcium levels (humoral control).

Transport of Hormones

  • Hormones travel through blood and are generally hydrophilic, allowing for easy mixing with blood plasma.

  1. Hydrophilic Hormones: Monoamines and peptides that mix easily in aqueous solutions.

  2. Hydrophobic Hormones: Steroids and thyroid hormones that require transport proteins (e.g. albumins and globulins) for circulation and to extend half-life.

Example of a Hydrophobic Hormone

  • Cortisol: A steroid hormone that requires transport proteins in the bloodstream.

Adrenal Medulla

  • Fast stress response due to direct stimulation by neurons (neural stimulation).

Effects of Pituitary Tumors

  • Hypersecretion of TSH can lead to symptoms such as hyperthyroidism and weight loss.

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Hormone Receptors

  • Specialized proteins or glycoproteins located on cell membranes, cytoplasm, or nucleus.

  • Critical role in activating specific target cells.

  • Lack of receptors can lead to diseases due to failure to engage metabolic pathways.

  • Peptides and Monoamines: Activate second messenger pathways.

  • Steroids and Thyroid Hormones: Influence gene activity.

Steroid and Thyroid Receptor Action

  • Steroids can diffuse through the cell membrane and typically activate receptors in the nucleus.

  • Thyroid hormones require active transport across the membrane before activating gene transcription.

Peptide Hormones

  • Cannot pass through the membrane, relying on cell surface receptors and secondary messenger systems (e.g., cAMP).

Second Messenger Action

  1. Cell surface receptors with G proteins activate phospholipase.

  2. Phospholipase cuts phospholipids producing inositol trisphosphate (IP3) and diacylglycerol (DAG).

  3. DAG activates kinases altering enzyme states.

  4. IP3 elevates intracellular Ca2+ levels by opening channels.

Example of Cellular Response

  • Oxytocin binds to uterine smooth muscle receptors.

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Amplification of Hormonal Signals

  • One hormone molecule can trigger multiple enzymatic reactions leading to a large-scale response.

Modulation of Hormonal Signals

  1. Up-regulation: Increases the number of receptors for greater sensitivity to hormones.

  2. Down-regulation: Decreases the number of receptors, reducing sensitivity during long-term exposure.

Hormone Interactivity

  • Permissive Effects: One hormone enhances the target organ's response to a second hormone.

  • Synergistic Effects: Two hormones acting together lead to a greater impact.

  • Antagonistic Effects: One hormone opposes the action of another.

Hormone Removal

  • Hormones metabolically cleared by the liver, kidneys, or target cells and excreted in bile or urine.

  • Metabolic Clearance Rate (MCR): Higher rate indicates a shorter half-life for hormones.

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CHAPTER 13: Insulin and Hormonal Action

Insulin Interaction with Target Cells

  • Insulin receptors are located on the cell membrane.

  • Binding results in glucose uptake into the cells.

Thyroid Hormone Interaction

  • Thyroid hormone receptors are located in the nucleus of the target cell.

  • Binds to initiate gene activation/metabolic increase.

Dietary Impacts on Diabetes

  • Poor diet can lead more commonly to Type II diabetes.

Digestive System Overview

Function of the Digestive System

  • Organ system that processes food, extracts nutrients, and eliminates waste.

  • Stages of Digestion:

    1. Ingestion: Selective intake of food.

    2. Digestion: Mechanical and chemical breakdown of food into a usable form.

    3. Absorption: Uptake of nutrient molecules into epithelial cells and subsequently into blood/lymph.

    4. Compaction: Absorbing water and consolidating indigestible residue into feces.

    5. Defecation: Elimination of feces.

Digestive Tract & Accessory Organs Components

  • Mouth: Involves teeth and salivary glands.

  • Esophagus, Stomach, Intestines: Main digestive tract components.

  • Accessory Organs: Include liver, gallbladder, pancreas.

Digestive Histology

  • Mucosa:

    • Epithelium: Simple columnar and stratified squamous.

    • Lamina Propria: Loose connective tissue.

    • Muscularis Mucosae: Thin smooth muscle to enhance surface area.

  • Submucosa: Thick, loose connective tissue.

  • Muscularis Externa: Two layers of muscle facilitating peristalsis.

  • Serosa: Simple squamous epithelium combined with areolar tissue.

  • Messenteries: Connective tissue sheets that suspend organs.

  • Omenta: Extensions of the mesentery associated with the stomach.

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Mouth and Pharynx

Mouth Components

  • Tongue: Facilitates manipulation of food texture and taste.

  • Teeth: Assist in mastication (chewing).

  • Palate: Separates oral and nasal cavities.

  • Uvula: Retains food in the mouth.

Salivary Glands and Functions

  • Parotid Gland: Secretes salivary amylase for starch digestion.

  • Submandibular Gland: Secretes mucus and helps with digestion.

  • Sublingual Gland: Produces lingual lipase for fat digestion.

Pharynx Function

  • Many muscles assist in swallowing, acting as a common passage for digestive and respiratory systems.

Pharyngeal Phases of Swallowing

  1. Oral Phase: Voluntary phase where the food bolus is pushed back.

  2. Pharyngeal Phase: Involuntary phase guided by the epiglottis and constrictor muscles.

  3. Esophageal Phase: Involves peristalsis to push food through the esophagus.

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Stomach

  • Muscular sac located inferior to the diaphragm, facilitates storage and digestion.

Key Features:

  • Chyme: Semi-liquid mixture formed post-digestion.

  • Regions of Stomach: Cardiac, fundus, body, and pyloric region.

  • Mucosal Structure:

    • Simple columnar epithelium lines the surface with gastric pits.

    • Contains parietal cells (produce HCl), chief cells (produce pepsinogen), and mucus cells (provide mucus).

Stomach Secretions

  • Gastric Juice: 2-3L produced daily.

  • HCl: Activates pepsin and begins protein digestion.

  • Pepsin: Zymogen activated by HCl, digests proteins into shorter peptides.

  • Gastric Lipase: Digests small amounts of fat.

Stomach Protection

  • Protective mechanisms include alkaline mucus and tight junctions to prevent self-digestion.

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Liver

  • Largest gland and second-largest organ, responsible for a multitude of metabolic processes.

Structure:

  • Composed of 4 lobes: right, left, quadrate, and caudate.

    • Hepatic Lobules: The functional units containing hepatocytes that detoxify and produce bile.

    • Sinusoids and Portal Triad: Blood filtering structures within lobules.

Functions of Liver

  • Produces bile: Assists in fat digestion, also processes nutrients.

  • Metabolism: Glucose is processed for energy or stored as glycogen, and toxins/drugs are broken down.

Gallbladder

  • Stores and concentrates bile to potentiate fat digestion.

Pancreas

  • Primarily an exocrine gland producing alkaline enzymes to assist digestion.

Hormonal Regulation of Digestion

  • Hormones secreted by duodenum include secretin and cholecystokinin (CCK) which regulate bile and pancreatic juice secretion.

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Small Intestines

Functions

  • Central site of chemical digestion and nutrient absorption.

  • Duodenum: Receives chyme and neutralizes stomach acid.

  • Jejunum & Ileum: Involved in nutrient absorption and bile acid reabsorption.

Structural Features

  • Villi: Finger-like projections that enhance surface area for absorption.

  • Lacteals: Part of the lymphatic system that absorbs digested fats.

  • Microvilli and Brush Border: Microscopic structures that increase absorptive area and provide digestive enzymes.

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Digestion Process

Carbohydrate Digestion

  • Amylases: Enzymes from salivary glands and pancreas hydrolyze starches into glucose.

  • Absorption: Glucose absorption occurs via co-transport with sodium ions and facilitated diffusion into capillaries.

Protein Digestion

  • Proteases: Enzymes like pepsin (in stomach) and trypsin (in duodenum) convert proteins to peptides and amino acids.

Fat Digestion

  • Lipases: Enzymes that further break down emulsified fats into monoglycerides and free fatty acids for absorption.

  • Emulsification: The process where fats are broken down into smaller droplets coated with bile salts for easier digestion.

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Fat Transport

Chylomicron Formation and Function

  • Chylomicrons are created within intestinal cells and released into the lymphatic system, playing a key role in fat transport into the bloodstream.

  • Transport mechanisms also include diffusion and facilitated pathways through intestinal membranes.

Large Intestine Function

  • Hosts a diverse gut microbiome aiding in fiber digestion and vitamin production.

  • Primary functions include water and electrolyte reabsorption, and formation of feces (70% water, 25% solids).

  • Defecation Mechanisms: Controlled by both voluntary and involuntary sphincters.

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CHAPTER 15: Metabolism

Cellular Metabolism Overview

  • Cells with little or no oxygen rely heavily on anaerobic glycolysis to produce ATP.

Lipogenesis and Glucose Conversion

  • Glucose serves as a precursor for fat through lipogenesis when excess calories are consumed.

Respiratory System Overview

Functions of the Respiratory System

  • Responsible for gas exchange, communication, olfaction, and maintaining acid-base balance in body fluids.

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Respiratory Tract Structure

Conducting Zone

  • Portions include:

    • Upper respiratory components: nostrils, nasal cavity, and larynx.

    • Helps filter, warm, and humidify incoming air.

Respiratory Zone

  • Contains alveoli for gas exchange.

  • Composed of small air sacs that permit diffusion of gases like oxygen and carbon dioxide effectively.

Specific Structures of the Respiratory System

  • Nasal: Ciliated epithelium to trap debris, while olfactory epithelium detects odors.

  • Pharynx: Muscular funnel connecting nasal cavity to larynx divided into nasopharynx, oropharynx, and laryngopharynx.

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Larynx and Bronchial Tree

Larynx Functions and Structures

  • Prevents choking and controls sound production.

  • Composed of various cartilages including the epiglottis that directs food away from the trachea.

Trachea Structure

  • “Windpipe” comprising C-shaped cartilaginous rings for structural support during breathing.

  • Lined with pseudostratified epithelium to help move mucus upwards.

Lung Anatomy

  • Lungs consist of multiple lobes: three on the right and two on the left, structures including the bronchial tree where gas exchange occurs.

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Pulmonary Ventilation

  • Inhalation: Diaphragm contracts increasing thoracic volume, lowering pressure to draw air in.

  • Expiration: Usually passive unless actively forced via abdominal muscles.

Neural Control of Breathing

  • Regulated primarily by respiratory centers in the brain including the medulla oblongata and pons which modulate the rhythm and depth of breath.

  • Dorsal and ventral respiratory groups interact to maintain homeostasis in breathing patterns based on physiological demands.

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Gas Exchange

  • Gas exchange occurs via diffusion across respiratory membranes in alveoli, with O2 and CO2 moving passively according to concentration gradients.

  • Carbon Dioxide Transport Mechanisms: Bicarbonate ions primarily, with hemoglobin and plasma transport as additional methods.

Buffer Systems in Blood

  • Maintain pH balance through mechanisms like the bicarbonate buffer system.

  • Changes in pH from respiratory disturbances remind the delicate interplay between respiratory function and metabolic needs.

Respiratory & Metabolic Disorders

  1. COPD: A group of diseases leading to long-term airway obstruction.

  2. Chronic Bronchitis: Inflammatory disease leading to excess mucus and decreased gas exchange.

  3. Emphysema: Destruction of alveolar walls decreases surface area for gas exchange.

  4. Asthma: Characterized by narrowing of airways, excessive mucus, and difficulty breathing.

  5. Lung Cancer: A major cause of death with strong links to smoking and various histological types.