Endocrine System
- Interacts with the Nervous System
o To coordinate and integrate the activity of Body Cells
o The Nervous System Regulates the Activity of Muscles and Glands via Electrochemical
Impulses delivered by Neurons
Organs responds within Milliseconds
- Increases Metabolic Activity by means of Hormones
o Chemical Messengers released into the Blood
o Binding of hormone into cellular receptors initiates responses
Typically occur after a lag period of seconds or even days
Once initiated, Responses tend to be more Prolonged than those induced by the
Nervous System
Hormones have Widespread and Diverse Effects
- Orchestrates Processes that go for Long Periods in some Instances
Nervous System Control Hormonal System Control
Information is conveyed in a form of Electrical Information Conveyed in a form of Chemical
Pulse Messengers
Axons and Dendrites Transmit Information Information is Transmitted through Blood
through a Coordinated Effort
Flow of Information is Rapid and Response is Flow of Information Travels Slowly and Response
Quick is Slow
Short-lived Effects Prolonged Effects
Hormones
- Integrated and Controlled Major Processes
o Reproduction
o Growth and Development
o Mobilization of Body Defenses
o Maintenance of Electrolyte, Water, and Nutrient Balance of the Blood
o Regulation of Cellular Metabolism and Energy Balance
- Long Distance Chemical Signals
- Travels in Blood and Lymph
- Autocrine
o Chemicals that effect on the same cells that secrete them
- Paracrine
o Acts on Neighboring cells
- Begins with the Binding of Hormones to Receptors
- Lipid-Soluble Hormones
o Enters target cell easily
Can Pass through the Plasma Membrane
o Hormone Binds to an Intercellular receptor in the Cytosol or the Nucleus
Receptor alters Gene Expression
If Gene is turned On
o mRNA produces and Directs Synthesis of new Proteins
Often Enzymes
If Gene is turned Off
o mRNA Synthesis is Halted
o Levels of Gene’s Protein will Decline
o This mode of action is Slower
- Water-Soluble Hormones
o Cannot easily pass through the Cell
o Receptors are located outside of the Plasma Membrane
o Binds to the Receptor and Never Enters the Cell
o Also called as the First Messengers
o Delivers message only as far as the Plasma Membrane
o A 2nd Messenger must relay the message and bring about a Response
Cyclic AMP (cAMP)
Most common 2nd Messengers
Growth Hormones (GH)
- Direct Actions
o Stimulates Liver, Skeletal Muscle, Bone, and Cartilage Cells
To Produce Insulin-like Growth Factors
Mediate the indirect, largely anabolic effects of GH
- Acts Directly on other Tissue Cells
o To Promote Fat Break-down
Lipolysis
o Release from Adipose Tissues
o Hinder Glucose Uptake from the Blood by the Tissue Cells
Renin
- When released into the Blood
o Acts upon Angiotensinogen
A Circulating Substrate
Undergoes Proteolytic Cleavage to form Angiotensin I
Vascular Endothelium
- Has an Enzyme called Angiotensin Converting Enzyme (ACE)
o Cleaves of 2 Amino Acids to form Octapeptide
Angiotensin II
Angiotensin II
- Causes Vasoconstriction
o Increases systemic vascular resistance and arterial pressure
- Stimulates Adrenal Cortex
o To release Aldosterone
Acts on Kidney to Increase Sodium and Fluid Retention
- Stimulates Vasopressin
o Increases Fluid Retention by the Kidneys
- Stimulates Thirst Centers
- Facilitates Norepinephrine Release
- Stimulates Cardiac and Vascular hypertrophy
Glands
- 2 types of glands
o Exocrine Glands
Produce Non-Hormonal Substances (Sweat, Saliva)
Have Ducts
Substances are rooted to a Membrane Surface
o Endocrine Glands
Aka “Ductless Glands”
Produce Hormones
Lack Ducts
Releases Hormones into the surrounding Tissue Fluid
Typically have a Rich Vascular and Lymphatic Drainage that receive Hormones
Endocrine Glands
- Pituitary, Thyroid, Parathyroid, Adrenal, Pineal, and Thymus Glands
- Hypothalamus
o Neuroendocrine Organ
o Neural Function
Produces and Releases Hormone
- Major Endocrine Glands
o Pancreas and Gonads
Ovaries and Testes
- 3 types of Endocrine Gland Stimuli
o Humoral Stimulus
Low Blood Calcium Levels Trigger Parathyroid Hormone Release from
Parathyroid Glands
o Neural Stimulus
Stimulation of the Adrenal Medullary Cells by Sympathetic Nerve System Fibers
Triggers the release of Catecholamines to the Blood
o Hormonal Stimulus
Hormones released by Hypothalamus
Stimulates the Anterior Pituitary to release Hormones
o Stimulates other Endocrine Organs to Secrete Hormones
- Hypothalamic Neurons in the Supraoptic and Paraventricular Nuclei
o Synthesize ADH and Oxytocin
- Neurons in the Ventral Hypothalamus
o Have Short Axons that Discharge
Releases and Inhibits Hormones
- These Hormones Influence the Adenohypophyseal secretory Cells
o To release or to not release their hormones
Hormones and Functions
Thyrotropin-Releasing Hormone (TRH) Stimulates Secretion of TSH and Prolactin
Corticotropin-Releasing Hormone (CRH) Causes Release of ACTH
Growth Hormone-Releasing Hormone (GHRH) Causes Release of Growth Hormone
Growth Hormone Inhibitory Hormone (GHIH) Inhibits Release of Growth Hormone
aka Somatostatin
Gonadotropin-Releasing Hormones (GnRH) Causes Release of LH and FSH
Dopamine or Prolactin-Inhibiting Factor (PIF) Inhibits Release of Prolactin
Growth Hormone (GH) Stimulates Protein Synthesis and Overall growth
of Most Cells and Tissues
Thyroid-Stimulating Hormone (TSH) Stimulates Synthesis and Secretion of Thyroid
Hormones
Adrenocorticotropic Hormone (ACTH) Stimulates Synthesis and Secretion of
Adrenocortical Hormones
Prolactin Promotes Development of Female Breasts and
Secretion of Milk
Follicle-Stimulating Hormone (FSH) Causes Growth of Follicles in the Ovaries and
Sperm Maturation in Sertoli Cells of Testes
Luteinizing Hormone (LH) Stimulates Testosterone Synthesis in Leydig Cells
of Testes
Stimulates Ovulation
Formation of Corpus Luteum
Estrogen and Progesterone Synthesis in Ovaries
Antidiuretic Hormone (ADH) Increases Water Reabsorption in the Kidneys
Aka Vasopressin Causes Vasoconstriction
Increased Blood Pressure
Oxytocin Stimulates Milk Ejection from Breast and Uterine
Contractions
Thyroxine (T4) and Triiodothyronine (T3) Increases the Rates of Chemical Reactions in
most Cells
Increases Metabolic rate
Calcitonin Promotes Deposition of Calcium in the Bones
Decreases Extracellular Fluid Calcium Ion
Concentration
Cortisol Multiple Metabolic Functions for Controlling
Metabolism of Proteins Carbohydrates, and Fats
Also has anti-inflammatory Effects
Aldosterone Increases Renal Sodium Reabsorption, Potassium
Secretion, and Hydrogen Ion Secretion
Norepinephrine, Epinephrine Increases Heart rate and Blood Pressure through
Vasoconstriction
Insulin Promotes Glucose Entry in many cells
Controls Carbohydrate Metabolism
Glucagon Increases Synthesis and Release of Glucose from
the Liver into the Body Fluids
Parathyroid Hormone Controls Serum Calcium Ion Concentration by
Increasing Calcium Absorption by the Gut and
Kidneys
Releases Calcium in the Bones
Testosterone Promotes Development of Male Reproductive
System and Male Secondary Sexual
Characteristics
Estrogens Promotes Growth and Development of Female
Reproductive System, Female Breasts, and
Female Secondary Sexual Characteristics
Progesterone Stimulates Secretion of “Uterine Milk”
Promotes Development of Secretory Apparatus
of Breasts
Human Chorionic Gonadotropin (HCG) Promotes Growth of Corpus Luteum and
Secretion of Estrogen and Progesterone by the
Corpus Luteum
Human Somatomammotropin Helps Promote Development of some Fetal
Tissues as well as the Mother’s Breasts
Renin Catalyzes Conversion of Angiotensinogen to
Angiotensin I (Acts as Enzyme)
1.25-Dihydroxycholecalciferol Increases Intestinal Absorption of Calcium and
Bone Mineralization
Erythropoietin Increases Erythrocyte Production
Atrial Natriuretic Peptide (ANP) Increases Sodium Excretion by Kidneys
Reduces Blood Pressure
Gastrin Stimulates HCI Secretion by Parietal Cells
Secretin Stimulates Pancreatic Acinar Cells
To Release Bicarbonate and Water
Cholecystokinin (CCK) Stimulates Gall Bladder Contraction and Release
of Pancreatic Enzymes
Leptin Inhibits Appetite
Stimulates Thermogenesis
