Week 5 · Lecture Slides · Endocrine

Endocrine System.

Seven slides on chemical messaging at distance: hormone mechanisms, the pituitary-hypothalamus axis, major glands, feedback loops, and clinical disorders.

Practice these cards

Core concept

Endocrine System

What you'll do

  • Move through six concept slides
  • Three slides have a drawable canvas
  • Toolbar: pen color, size, eraser, undo, add image, save
  • Drop in your own anatomy images to label them
Endocrine Signaling

Hormone types

Peptide (surface receptor)
Amino acid-derived
Steroid (intracellular)
Thyroid (intracellular)

Major glands

Hypothalamus + pituitary
Thyroid + parathyroids
Adrenals
Pancreas + gonads

Definition

What the Endocrine System Does

Chemical messaging at distance

  • Hormones: chemical messengers in the bloodstream
  • Target only cells with matching receptors
  • Slow onset, long duration (vs nervous system: fast, brief)
  • Endocrine = ductless, secrete into blood
  • Exocrine = ducted (e.g., sweat, salivary)
  • Paracrine = local; autocrine = self
  • Released in response to humoral, neural, or hormonal stimuli
Takeaway: endocrine signaling is precise even though hormones go everywhere. The receptor is what makes it specific. Same hormone, different receptors = different effects.

Mechanisms

Hormone Types & Action

Two big classes

  • Peptide/protein + amino acid-derived hormones
  • Water-soluble; cannot cross membrane
  • Bind cell-surface receptors, use second messengers (cAMP, IP3)
  • Examples: insulin, GH, ADH, oxytocin, epinephrine, most others
  • Steroid + thyroid hormones
  • Lipid-soluble; cross membrane
  • Bind intracellular receptors, regulate gene expression
  • Slow but lasting effects
Draw: a cell with two pathways side by side. Left: peptide hormone binding surface receptor, activating G-protein → cAMP → effect. Right: steroid hormone passing through membrane, binding nuclear receptor, going to DNA → transcription.

Pituitary

The Pituitary & Hypothalamus

The master link

  • Anterior pituitary (adenohypophysis): glandular tissue
  • Produces: GH, TSH, ACTH, FSH, LH, PRL
  • Controlled by hypothalamic releasing/inhibiting hormones via portal system
  • Posterior pituitary (neurohypophysis): neural tissue
  • Stores + releases oxytocin and ADH (made in hypothalamus)
  • Hypothalamic-pituitary axis = control center
Takeaway: mnemonic for anterior pituitary hormones: FLAT PiG = FSH, LH, ACTH, TSH, Prolactin, GH. Posterior just stores two: ADH and oxytocin, both made upstream.

Glands

Major Endocrine Glands

Locate + label

  • Pineal (brain, melatonin)
  • Hypothalamus + pituitary (brain)
  • Thyroid (neck, T3/T4 metabolism, calcitonin)
  • Parathyroids (behind thyroid, PTH raises Ca²⁺)
  • Thymus (thorax, T cell maturation)
  • Adrenals (atop kidneys, cortex + medulla)
  • Pancreas (insulin/glucagon)
  • Gonads (testes/ovaries, sex hormones)
Draw: a body outline with each major endocrine gland in approximate location. Label each gland and write the main hormone(s) it makes next to it. Use color to group related glands (HPA axis, gonadal, etc).

Feedback

Negative Feedback Loops

How balance is maintained

  • Hypothalamus releases TRH
  • Anterior pituitary releases TSH
  • Thyroid releases T3/T4
  • T3/T4 inhibit TRH + TSH (long + short loops)
  • Same pattern: CRH → ACTH → cortisol → inhibits CRH/ACTH
  • GnRH → FSH/LH → sex hormones → inhibits GnRH
  • Disruption: ↓ target hormone removes brake, pituitary overshoots
Draw: a feedback loop diagram. Three boxes top to bottom: hypothalamus → pituitary → target gland → hormone. Add a long arrow showing the hormone inhibiting the top of the loop. Apply to the HPT (thyroid) axis.

Clinical

Endocrine Disorders

Excess or deficiency

  • Type 1 diabetes autoimmune β-cell destruction, no insulin
  • Type 2 diabetes insulin resistance + relative deficiency
  • Graves autoantibodies stimulate TSH receptor → hyperthyroid
  • Hashimoto autoimmune hypothyroid
  • Cushing excess cortisol (often pituitary or adrenal tumor)
  • Addison adrenal cortex failure, low cortisol + aldosterone
  • Acromegaly GH excess in adults
  • SIADH too much ADH; diabetes insipidus too little
Takeaway: pattern: too much hormone vs too little, and at which level (primary at gland, secondary at pituitary, tertiary at hypothalamus). Lab pattern of hormone + tropic hormone localizes the lesion.