Week 12 Content Flashcards
The Endocrine System
Regulates body functions with the nervous system
Ductless glands secrete hormones
Endocrinology: The study of hormones and glands
Endocrine System Functions
Produce, release, and distribute hormones through bloodstream to targets
Regulate mood, growth, metabolism, and reproduction
Hormones
Chemical messenger produced by endocrine glands
- Specific
Maintain homeostasis
Controlled by feedback mechanisms
- Varied effects
Classes of Hormones
- Amino acid-based hormones
- Steroids
Amino Acid-based Hormones
Derived from amino acids
Water soluble
Bind to receptors on cell surface
- ie; Thyroid hormones, insulin
Steroids
Derived from cholesterol
Lipid soluble
Pass through cell membrane to bind to receptors
- ie; Cortisol, estrogen, testosterone
Control of Hormone Secretion
- Humoral stimulus
- Neural stimulus
- Hormonal stimulus
Humoral Stimulus
Simplest
Secretion triggered by ion or nutrient levels in blood
Maintain homeostasis
- Regulate body without external signals
- ie; Parathyroid monitors calcium and secretes a hormone to reverse calcium decline
Feedback Loops
Mechanisms regulate hormone secretion to maintain homeostasis
Adjusting hormone levels based on blood concentrations
- Falls below minimum = More hormone secreted
- Exceeds maximum = Production stops
Negative Feedback
Most common
Hormone secretion inhibited once desired level is reached
- ie; Blood glucose
Positive Feedback
Less common
Stimulus causes release of more hormone until a specific event occurs
- ie; Oxytocin during childbirth
Neural Stimulus
Nerve fibers stimulate endocrine gland to release hormones
Sympathetic fibers stimulate adrenal medulla
- Triggers release of epinephrine and norepinephrine
- ‘Fight or Flight’ response
Hormonal Stimulus
Hormones from one gland trigger release of another
- ie; Hypothalamus secretes hormones - Stimulates pituitary - Stimulates other glands
Different Stimulus Diagram
Pure Endocrine Organs
- Pituitary gland
- Pineal gland
- Thyroid and parathyroid glands
- Adrenal glands (including adrenal cortex and adrenal medulla)
Organs with Many Endocrine Cells
- Pancreas
- Thymus
- Gonads (ovaries and testes)
- Hypothalamus (neuroendocrine organ)
Organs with Some Endocrine Cells
- Heart
- Digestive tract
- Kidneys
- Skin
Pituitary Gland
Master gland
Secretes 9 major hormones
Attached to hypothalamus by the infundibulum
1. Anterior lobe: Adenohypophysis
2. Posterior lobe: Neurohypophysis
Pituitary Gland Function
Secrete hormones that influence…
- Growth
- Metabolism
- Stress response
- Reproduction
- Water balance
Anterior Lobe Divisions
- Pars distalis
- Pars intermedia
- Pars tuberalis
Posterior Lobe Divisions
- Pars nervosa
- Infundibulum
Pars Distalis
Largest
Produces and secretes 6 different hormones
Pars Distalis - Tropic Hormones
Regulate hormone secretion by other glands
1. Growth hormone (GH)
2. Prolactin (PRL)
3. Thyroid-stimulating hormone (TSH)
4. Adrenocorticotropic hormone (ACTH)
5. Follicle stimulating hormone (FSH)
6. Luteinizing hormone (LH)
Mnemonic: Guys, Please, That Ain’t Freakin’ Love
Pars Intermedia
Thin layer between anterior and posterior lobes
Less active in humans, produces melanocyte-stimulating hormone (MSH) in some animals
Region not well-defined in adults
Pars Tuberalis
Protective sheath surrounding infundibulum
- Supports pituitary function
Connects to the hypothalamus
Regulates seasonal rhythms in some species
Hypothalamic Control of Anterior Lobe
Master regulator of pituitary gland
Sends chemical signals through the bloodstream to anterior pituitary
1. Releasing hormones
2. Inhibiting hormones
Releasing Hormones
Produced by hypothalamus
Stimulate anterior pituitary to release specific hormones
Inhibiting Hormones
Produced by hypothalamus
Suppress hormone release from anterior lobe
- Prevent over-secretion
How Hormones Reach the Body
- Hormones released by hypothalamic neurons
- Enter primary capillary plexus in hypothalamus
- Flow through hypophyseal portal veins to anterior pituitary
- Hormones enter bloodstream from secondary capillary plexus in anterior pituitary
- Act on target organs
Posterior Lobe
Neural tissue
Does not produce hormones
Stores and releases hormones produced in hypothalamus
1. Paraventricular nucleus
2. Supraoptic nucleus
Posterior Lobe Hypothalamic Connection
Hormones travel down axons to posterior lobe
- Hypothalamohypophyseal tract
Stored in axon terminals
Released into the bloodstream
Hormones Released by Posterior Lobe
Oxytocin
- Produced in paraventricular nucleus
- Uterine contractions, milk ejection, social bonding
Antidiuretic hormone (ADH, Vasopressin)
- Produced in supraoptic nucleus
- Conserves water, raises blood pressure
Pineal Gland
Small gland on roof of diencephalon
Between hemispheres near the thalamus
Regulates sleep-wake cycles and biological rhythms
Melatonin
Secreted by pineal gland in response to darkness
Light detected by retina inhibits production via suprachiasmatic nucleus (SCN) of the hypothalamus
Thyroid Gland
Anterior neck
2 lobes and a central isthmus
Largest purely endocrine gland
Thyroid Gland Functions
Regulates metabolism
Supports growth
Maintains homeostasis
- Influences heart rate, body temperature, and weight
Produces hormones
Hormones Produced by Thyroid
Thyroid Hormones (TH)
- T3: Active form, regulates metabolism
- T4: Converted to T3 in target tissues
Calcitonin: Lowers blood calcium, inhibits bone breakdown, enhances calcium uptake
Control of the Thyroid
Regulated by the hypothalamus-pituitary-thyroid axis
1. Hypothalamus releases TRH (Thyrotropin-releasing hormone)
2. TRH prompts the pituitary to secrete TSH (Thyroid-stimulating hormone)
3. TSH stimulates the thyroid to release T3 and T4
The Parathyroid Glands
4 small glands on posterior thyroid
Regulate calcium balance
Produce parathyroid hormone (PTH)
- Raises blood calcium
- Opposes calcitonin
Parathyroid Gland Functions
Calcium homeostasis
- Bone resorption
- Calcium absorption
- Calcium retention
Adrenal Glands
Superarenal glands
- On top of each kidney
- Supplied by 60 superarenal arteries
- Sympathetic fibers
Adrenal cortex and adrenal medulla
Adrenal Cortex
Outer layer
Produces steroid hormones (Corticosteroids)
- Aldosterone, cortisol, and androgens
Adrenal Medulla
Cluster of neurons
Sympathetic nervous system
‘Fight or Flight’ response
Produces catecholamines
- Epinephrine and norepinephrine
Stress Reponse Diagram
Pancreas
Posterior abdomen wall
- Endocrine cells: Regulate blood sugar (pancreatic islets/Islets of Langerhands)
- Exocrine cells: Secrete digestive enzymes (Acinar cells)
Pancreas Anatomy
- Head
- Neck
- Body
- Tail
Key Hormones Secreted by Pancreas
- Insulin
- Glucagon
- Somatostatin
- Pancreatic polypeptide
Insulin
Produced by beta cells
Lowers blood sugar by promoting glucose uptake into cells
Storaged as glycogen in liver and muscles
- Released after meals
Glucagon
Produced by alpha cells
Raises blood sugar
Stimulates glycogen breakdown and gluconeogenesis in liver
Released during fasting
Somatostatin
Produced by delta cells
Inhibit secretion of insulin and glucagon
- Regulate hormone activity
Pancreatic Polypeptide
Secreted by pancreatic polypeptide cells (F cells)
Regulates pancreatic function
- Influences appetite and digestion
Regulates hormone secretion
Blood Sugar Regulation
Pancreas maintains blood sugar homeostasis
After eating: Insulin lowers blood
During fasting: Glucagon raises blood sugar
Thymus
Anterior thorax
Immune organ
- Site of T lymphocyte development
Maturation stimulated by…
- Thymopoietin
- Thymosin
Male Gonads
Main sources of sex hormones
Produced in testes
Androgens are masculinizing
- Testosterone and dihydrotestosterone (DHT)
Masculinizing Hormone Functions
Primary male sex organs (penis, testes)
Secondary sex characteristics (ie; facial hair, deeper voice, increased muscle mass)
Spermatogenesis
Female Gonads
Main sources of sex hormones
Produced in ovaries
Estogen (Secondary sex characteristics)
Progesterone (Prepares uterus for pregnancy)
Feminizing Hormone Functions
Sex characteristics (breast development, wider hips, fat distribution)
Bone density
Pregnancy maintenance
Menstrual cycle regulation
Hypothalamic-Pituitary-Gonadal Axis
Other Regions with Endocrine Structures
Heart: Atria contain atrial natriuretic peptide (ANP)
GI tract: Enteroendocrine cells secrete hormones
Kidneys: Produce renin and secrete erythropoietin
Skin: Converts cholesterol into vitamin D precursor
Pituitary Disorders
Gigantism
- Hypersecretion of growth hormone (GH) in children
- Excessive growth
Pituitary dwarfism
- Hyposecretion of GH
- Reduced growth but proportional body size
Diabetes Insipidus
- Pars nervosa produces insufficient antidiuretic hormone (ADH)
- Excessive thirst, large amount of dilute urine
Pancreas Disorders
Diabetes mellitus
- Insufficient secretion of insulin
- Body cells resistant
Type 1 diabetes: Sudden onset (age<15), autoimmune beta cell destruction, requires insulin therapy
Type 2 diabetes: Gradual onset (age >40), insulin resistance; managed with diet, exercise and medication
Thyroid Gland Disorders
Graves’ disease
- Common hyperthyroidism
- Immune overstimulation of thyroid
- Symptoms: Nervousness, weight loss, sweating, rapid heart rate, bulging eyes
Myxedeme
- Severe hyperthyroidism in adults
- Autoimmune system destroys thyroid tissue
- Symptoms: Fatigue, weight gain, cold sensitivity, dry skin, hair thinning, swelling
Cretinism
- Congenital hypothyroidism in children
- Short stature, thick tongue, delayed speech, intellectual disabilities’
Endemic goiter
- Dietary iodine deficiency
- Enlarged thyroid gland
Adrenal Cortex Disorders
Cushing’s syndrome
- Excess glucocorticoids (ie; cortisol)
- Pituitary tumor or prolonged corticosteroid use
- Symptoms: Weight gain, fat pads, muscle weakness, high blood pressure and blood sugar
Addison’s disease
- Hyposecretory disorder of the adrenal cortex (aldosterone, cortisol)
- Symptoms: Fatigue, low blood pressure, salt craving, hyperpigmentation, weight loss, abdominal pain
GH and PRL Diagram
TSH and ACTH Diagram
FSH and LH Diagram
ADH and Oxytocin Diagram
Lymphatic System
Maintains fluid balance
Absorbs fats from the digestive system
Supports immune function
Collects tissue fluid (lymph), filtered in lymph nodes
Immune System
Network of cells, tissues, and organs
Defends against infections
Confers immunity (innate and adaptive)
Comparison of Systems Diagram
Lymphatic Vessels
Collect fluid from tissues and return it to the bloodstream
Transport fluid to large veins near the neck
Tissue fluid inside called lymph
Lymph flows toward the heart
Orders of Lymphatic Vessels
- Lymph capillaries
- Collecting lymphatic vessels
- Lymph trunks
- Lymph ducts
Lymph Capillaries
Smallest lymph vessels
First to receive lymph
Near blood capillaries
Highly permeable
Function of Lymphatic Capillaries
Collect excess fluid from connective tissue
Minivalve flaps open to allow fluid entry
Tissue fluid, proteins, bacteria, viruses, and cancer cells
Lacteals
Specialized lymphatic capillaries in small intestine villi
Absorb digested fats
Transport fatty lymph (chyle)
Collecting Lymphatic Vessels
Collect from lymph capillaries
Run alongside blood vessels
Contain more valves than veins
- One-way flow to lymphatic trunks
Flow of Lymph
- Bulging skeletal muscles during movement
- Pulsing nearby arteries
- Contractions of tunica media in lymphatic vessels
Lymph Nodes
~500 in the body along collection vessels
Cluster in cervical, axillary, and inguinal region
Dense outer capsule with internal network
Structure of Lymph Nodes
Capsule: Outer covering
Sinus: Channels inside, slows lymph flow
Cortex: Outer region, immune activation
Trabeculae: Connective tissue dividing segments
Medulla: Inner region with lymphocytes and macrophages, final filtration
Hilum: Indented exit for blood vessels and lymph
Function of Lymph Nodes
Cleanse lymph of pathogens
Trap bacteria, viruses, and foreign particles
Identify and destroy pathogens
Trigger immune response, swell
Lymph Flow through Lymph Nodes
Lymph enters via afferent vessels, pass through hilum
Exit through efferent vessels
Filtration and immune surveillance
Cleansed lymph returns to bloodstream
Deep Lymph Nodes
Near major blood vessels and organs
- Tracheobronchial, aortic, and iliac lymph nodes
Filter lymph from internal organs and deeper tissues
Lymph Trunks
Collect lymph from converging lymphatic vessels
- Lumbar: Lower limbs
- Intestinal: Digestive organs
- Bronchomediastinal: Thoracic organs
- Subclavian: Upper limbs and thoracic wall
- Jugular: Head and neck
Lymphatic Ducts
Trunks merge into lymphatic ducts
1. Thoracic duct
2. Right lymphatic duct
Return lymph to bloodstream
Maintain fluid balance, support immune function
Cisterna Chyli
Sac-like lymph reservoir in abdomen
Junction of lumbar and intestinal trunks
Collects lymph and chyle before entering the thoracic duct
Thoracic Duct
Largest lymphatic vessel, drains majority of body
Receives lymph from cisterna chyli
Ascends along vertebral bodies
Empties into venous circulation at junction of left internal jugular and left subclavian veins
Right Lymphatic Duct
Drains lymph from right arm, right chest, and right head/neck
Empties into bloodstream at right internal jugular and subclavian veins
Regional Lymph Nodes Diagram
The Immune System
Recognizes and targets foreign molecules
Destroys pathogens
Lymphocytes coordinate defence in lymph nodes
Involves immune cells, lymphoid tissues, and organs
Immune Cells
- Lymphocytes
- Macrophages
- Neutrophils
- Natural killer cells
- Dendritic cells
Lymphocyte Formation and Maturation
White blood cell formed in red bone marrow
B cells mature in bone marrow, T cells mature in thymus
Become immunocompetent, recognize specific antigens
Lymphocyte Function
B and T cells migrate to spleen and lymph nodes
B cells target pathogens in blood/lymph (humoral response)
T cells target infected cells (cell-mediated response)
Macrophages
White blood cells in lungs, liver, spleen, and lymph nodes
One of the first responders to infections
Engulf and digest pathogens, present antigens, trigger inflammation
Neutrophils
Most abundant white blood cell in innate immune system
In bloodstream, first cells to infection sites
Phagocytize, release enzymes, form pus
Short-lived, first responders
Natural Killer Cells
White blood cell in blood and tissues
Targets and destroys infected or cancerous cells
Releases cytotoxins
Rapid response, defense against infections and tumours
Dendritic Cells
In skin, mucosal surfaces, and lymphoid organs
Capture pathogens and foreign particles
Present antigens to T cells
Activate T cells adaptive immune response
Immune Response
Infection triggers inflammatory response
- Neutrophils respond first, then macrophages, then lymphocytes
Lymphocytes target specific antigens
Lymphoid Tissues
- Mucous membranes in digestive, urinary, respiratory, and reproductive tracts
- Mucosa associated lymphoid tissue (MALT) - Lymphoid organs (except thymus)
Lymphoid Organs
- Thymus (Primary)
- Red bone marrow (Primary)
- Lymph nodes (Secondary)
- Spleen (Secondary)
- Tonsils (Secondary)
- Peyer’s patches (Secondary)
- Appendix (Secondary)
Thymus Structure
Superior mediastinum
Two lobes in connective tissue capsule
Cortex: Immature T cell proliferation and differentiation
Medulla: T cell maturation, contains thymic corpuscles
Thymus Function
Site of T lymphocyte development
Secretes thymic hormones
Critical for adaptive immunity
Most active in childhood, atrophies with age
Red Bone Marrow
Found in spongy bone of flat and long bones
Contains blood vessels, hematopoietic stem cells, and support cells
Produce blood cells
B lymphocytes maturation
Lymph Nodes
Small structures along lymphatic vessels
Filter lymph
Destroy antigens
Activate B and T lymphocytes for immune response
Spleen
Largest lymphoid organ
Left side of abdomen
Stores blood
- Red pulp: Filters blood
- White pulp: Performs immune functions
Red Pulp of Spleen
Contains blood vessels and macrophages
Filter and remove damaged red blood cells
Surrounds white pulp
Splenic sinusoids and cords
Red Pulp Components
Splenic Cords: Contain macrophages and lymphocytes, filter old and damage red blood cells
Splenic Sinusoids: Slow blood flow, macrophages to remove damaged red blood cells
White Pulp of Spleen
Immune function of the spleen
Contains lymphocytes, detect and respond to infections
Activates B cells to produce antibodies and T cells to kill infected cells
Spleen Structure
Capsule: Dense connective tissue exterior
Trabeculae: Fibrous extensions supporting internal structure
Hilum of Spleen
Entry/exit point
Splenic artery: Enters, supplies oxygenated blood
Splenic vein: Exits, carries filtered blood
Lymphatic vessels and nerves: Pass through
Blood Flow through the Spleen
Splenic artery: Delivers oxygenated blood
Arterioles and capillaries: Blood flows into capillaries
Splenic sinusoids: Filters blood, removes damaged cells
Splenic vein: Drains filtered blood to circulation
Tonsils
Lymphoid tissue around the pharynx
Protect against pathogens entering the mouth of nose
Lymphocytes detect pathogens
Trapped in crypts
Tonsil Types
- Palatine tonsils: Lateral walls of oropharyx; the tonsils
- Pharyngeal tonsil (adenoids): Roof of nasopharyx
- Lingual tonsils: Posterior, dorsal surface on tongue
- Tubal tonsils: Near eustachian tube openings
Peyer’s Patches
Clusters of mucosa-associated lymphoid tissue (MALT) in ileum
Monitors gut pathogens, generate memory B and T cells
Rapid immune responses
Appendix
Small tube attached to cecum
Contains MALT, monitors pathogens
Stores beneficial bacteria, restores microbiome after infection
Active in childhood immunity; decreases with age
Lymphedema
Swelling in arms and legs, discomfort
Caused by damaged or removed lymph nodes
Poor lymph drainage, lymph build up, higher risk of infection
Lymphadenopathy
Swollen lymph nodes
Infections, autoimmune diseases, or lymphoma
Tender nodes in neck, armpits, or groin
Cancer of the Lymphatic System
Affects lymphocytes
Hodgkin’s lymphoma: Lymph node cancer
Non-Hodgkin’s lymphoma: Uncontrolled lymphocyte growth and spread
Symptoms: Swollen lymph nodes, fever, weight loss, night sweats, and fatigue
Tonsilitis
Inflamed tonsils
Viral (ie; adenovirus) or bacterial infections (ie; streptococcus)
Sore throat, fever, difficulty swallowing, and swollen lymph nodes
Immune System Disorders
Autoimmune diseases: Immune system attacks its own tissues (ie; Rheumatoid arthritis, type 1 diabetes, multiple sclerosis
Immunodeficiency disorders: Weakened immune system, prone to infections (HIV/AIDS)
Allergies: Overreaction to harmless substances (ie; food allergies, asthma, environmental)
Celiac disease: Immune response to gluten, damages small intestine
Lupus: Chronic autoimmune disease infecting multiple organs, causes joint pain, rashes, and organ damage
