Histology Skin, Urinary and Endocrine

• Protection
• Excretion
• Absorption
• Regulation of Body Temperature
• Sensory Reception

• Epidermis
o Derived from ectoderm
o Made of stratified squamous keratinized epithelium
• Found on the thickening of palms and soles
• Have 4 types of cells here
o Keratinocytes
• Largest
• Have 4-5 layers
• Characterized by presence of keratin
• Take 20-30 days for cells to reach the top
o Melanocytes
• Found in basal layer
• Derive from neural crest
• Make melanin (made of protect DNA from UV light) and localized in melanosomes (accumulation of melanin in vesicles)
• Secrete cytocrine
• Have epidermal-melanin unit (one keratinocyte and one melanocyte)
o Langerhans Cells
• Dendritic APC cells that come from bone marrow
• Found primarily in the stratum spinosum
• Found in skin, oral cavity, esophagus and vagina
• Have a dense nucleus, pale cytoplasm and long slender process
o Merkel Cells
• May Function as mechanoreceptor
• Have deeply indented nuclei
• Interspersed among keratinocytes (found in fingertips)
• Dermis
o Derived from Mesoderm and has varying thickness
o Made of dense irregular, collagenous connective tissue
o Has two layers:
• Papillary layer
 Made of loose connective tissue, lots of elastic and reticular fibers, is very vascular
 Has Meissner Corpuscles
• Pear-shaped, encapsulated mechanoreceptors
• Specialized for light touch
 Has Krause End Bulbs
• Has conjunctiva and mucous membranes
• Reticular layer
 Made of dense, irregular collagenous connective tissue
 Contains specialized epidermal invaginations
• Hair follicles, sebaceous glands, sweat glands, smooth muscle

• Technically not a layer of the skin
• Made of loose connective tissue
• Has differing thickness
• Contains a substantial amount of adipose tissue embedded in subcutaneous fascia
• Not found in the eyelids, penis and scrotum

• Dermal Ridges (Papillae)
o Raised ridges of dermis at interface with epidermis
• Epidermal Ridges
o Invaginations of epidermis into dermis
• Dermatoglyphs
o Fingerprints, that develop in utero

• Thick Skin (Hair-less)
o Has 5 cell layers
o Has NO hair, arrector pili muscle or sebaceous glands
o Has sweat glands
• Thin Skin (Hairy)
o Has 4 cell layers
o Has hair, arrector pili muscle, sebaceous glands and sweat glands

• Stratum Basale (Germinativum)
• Stratum Spinosum
• Stratum Granulosum
• Stratum Lucidum
• Stratum Corneum

• Amount of melanin and carotene
• Presence of blood vessels and the color of our blood
• The pigmentation of the skin has to do with the location and tyrosinase activity rather than the number of melanocytes
• White ppl: smaller and tightly localized around nucleus melanosomes
• Black ppl: larger melanosomes and widely dispersed

• Ruffini Corpuscles
o Encapsulated mechanoreceptor
o Respond to torsional forces
o Abundant in the soles of our feet
o Elongated fusiform shape
o Structurally similar to the Golgi Tendon Organ
• Pacinian Corpuscles
o Encapsulated mechanoreceptors
o Respond to deep pressure and vibration
o Found in walls of bladder, external genitalia and joint capsules

• Eccrine Sweat Glands
o Simple, coiled tubular glands
o Develop as invaginations of the skin
o Secretory portion: simple cuboidal, myoepthelial cells
o Duct: stratified cuboidal
• Apocrine Sweat Glands
o Larger than eccrine glands
o Secretory cells are cuboidal to low columnar
o Ducts open into canals of hair follicles
• Sebaceous Glands
o Secrete sebum: wax-like mixture of cholesterol and triglycerides
o Secretion is controlled by sex hormone
o Functions to maintain flexibility of hair and texture of skin
o Duct opens into hair canal or directly onto surface of skin
o Most abundant on face, scalp and forehead but found everywhere except palmar and plantar surfaces

• A filamentous, keratinized structure
• Two types
o Vellus
o Terminal

• Organs that grow hair
• Hair follicle is separated from epidermis by a thick basal lamina known as the glassy membrane
• The base of the hair follicle is called the hair root
• The root + ingrowth of dermis is called the hair bulb

• A smooth muscle attached to the connective tissue sheath and papillary layer of the dermis
• Contracting this muscle results in lifting of the hair and a bump of the skin→ goosebumps

• Anagen Phase
o Period of growth
o Scalp hair remains here for 6 years
• Categen Phase
o Brief period of shrinking
• Telogen Phase
o Final rest phase; mature hair is shed

• Nail Plate: Highly keratinized cells
• Nail bed: epidermis
• Nail Matric: Proliferative layers
• Nail Root: Contains the matrix
• Eponychium: Cuticle
• Lunula: White Crescent
• Hyponychium: Junction of nail bed with the skin

•• Regulate metabolic activities
• Homeostasis
• Causes effects by releasing hormones

• Isolated cells and cluster of cells in respiratory and digestive
o DNES
• Encapsulated endocrine glands
o Ductless, super vascularized
o Fenestrated Capillaries

• Amino-acid derivatives
o Thyroxine, Epinephrine, Norepinephrine
• Proteins and Polypeptides
o Insulin, Glucagon, Follicle-Stimulating Hormone
• Steroids and Fatty-Acyl Derivative
o Progesterone, Estrafdol, Testosterone, Cortisol

• Amino-acid derivatives
o Thyroxine, Epinephrine, Norepinephrine
• Proteins and Polypeptides
o Insulin, Glucagon, Follicle-Stimulating Hormone
• Steroids and Fatty-Acyl Derivative
o Progesterone, Estrafdol, Testosterone, Cortisol

• Produce hormones that regulate
o Growth
o Reproduction
o Metabolism

• Anterior and Posterior

• Pars Distalis
• Pars Intermedia
• Pars Tuberalis

• Median eminence
• Infundibulum
• Pars Nervosa

• Cells are arranged in cords and the secretory product is stored and released in vesicles
• Two cell types
o Chromophils and Chromophobes

• Two types of chromophil cells based on dye affinity
o Acidophils
• Somatotrophs secrete somatotrophin (Growth Hormone)
• Mammotrophs (Lactotrophs)
 Promote breast development and stimulate mammary glands to secrete milk
o Basophils
• Corticotrophs
 Secrete POMC, ACTH and lipotropic hormone
• Thyrotrophs
 Thyrotropin, TSH, Relase Thyroxine from thyroid gland
• Gonadotrophs
 FSH, LH (ICSH)

• Has colloid-containing cysts and some POMC secreting basophils
• Have alpha and beta melanocyte stimulating hormone

• Surround the hypophyseal stalk
• Have some gonadotropin secreting basophils

• Not really an endocrine organ or a gland
• Comes from Ectoderm
• Downgrowth of the hypothalamus
• Majority is the pars nervosa which stores hormones

• They are unmyelinated axons that connect the hypothalamus to the pars nervosa
• Secretory product is stored in Herring Bodies
• Have pituicytes (glial like cells)

• Oxytocin- stimulates contraction of uterine smooth muscle and smooth muscle like cells (myoepithlial etc)
• Vasopressin
o Regulates permeability of CD

• Set of capillaries from the superior hypophyseal artery that collect factors from the median eminence
o Portal veins drain this primary capillary plexus and deliver blood to secondary capillary plexus in pars distalis
• Collecting veins carry hormones away

• It is the terminus for hypothalamic neurons releasing control hormones
o These hormones control control the secretory function of acidophils and basophils in the pars distalis
• Ex. GRH, SRH, TSRH etc.

• Has a slight collagenous capsule
• Has two lobes and a connecting isthmus
• Septa divides lobes into lobules
• Secretory cells are arranged in follicles and the products are stored in the follicle lumen

• Has simple cuboidal or columnar epithelium
• Has a cavity filled with gel-like colloid
• Each follicle surround by thin strand of connective tissue with capillaries, lymphatics and nerves

• Principal cells
o Simple squamous to low columnar
o Secrete Thyroxine (T4) and T3 which stimulate metabloism
• Parafollicular cells (C Cells)
o Pale staining
o Larger than principal cells
o Secrete Calcitonin which decreases blood calcium levels

• Thyroid hormones stimulate gene transcription by binding to a receptor ends initiating a transcription factor

• Hyperplasia of follicular cells due to increased thyroxine production

• Hyperplasia due to iodine deficiency

• May result from iodine deficiency results in cretinism in children
• Can be treated with synthetic thyroxine

• Has 4 small glands
• Makes and secretes PTH
• Parenchyma is composed into cords of epithelial cells
• Had two cell types
o Chief Cells
• Slightly basophilic
o Oxyphil Cells
• More Acidophilic
• Not as many

• Acts on kidneys, bones and intestines to increase extracellular calcium

• Primary- Often cause by a tumor and results in elevated blood calcium levels
• Secondary- May develop in patients with Rickets (Due to vitamin d deficiency) results in low blood calcium levels

• Having low blood calcium, retention of calcium in bones and increased phosphorous resorption by the kidneys

• Embedded in adipose tissue
• Surrounded by a dense collagenous connective tissue capsule
• The right and left glands are not mirror images
o The left is a crescent shape while the right is pyramid shaped

• The adrenal cortex has a outer yellowish region
o Makes Corticosteroids (Mineralocorticoids and Glucocorticoids) from cholesterol
o Regulated by ACTH (from anterior pituitary)
o Parenchyma makes and secretes the steroid hormones without storing them
• Has 3 zones:
o Zona glomerulosa
o Zona fasciculate
o Zona Reticularis

• The adrenal medulla (arises from neural ectoderm)
o small, dark inner potion
o Regulated by the Sympathetic Nervous System
o Makes Catecholamines (Adrenaline and Noradrenaline)

• Synthesize the hormone from cholesterol and take the cholesterol into the cell as LDL from blood and store it in lipid droplets.
• Enzymes in the SER and mitochondira then convert the cholesterol into bioactive hormone

• It is the outer ring of cortical tissue
• The cells here are arranged in chords and clusters
• Cells are acidophilic and have abundant SER and are surrounded by capillaries

• Mineralocorticoids
o Regulate K+ and Na+ homeostasis
• Aldosterone
o Stimulates reabsorption of sodium by kidney
o Stimulates secretion of potassium in salivary glands
o Leads to uptake of water and increased blood pressure
• Deoxycorticosterone

• ACTH and Angiotensin II (when kidney volume is low)

• Central layer of the cortex
• Cells are arranged in longitudinal columns which are separated by sinusoidal capillaries
• Cells are light staining due to large accumulations of lipid known as spongiocytes

• Glucocorticoids- regulate carbohydrate, lipid and protein metabolism by stimulating glycogenesis and gluconeogenesis
• Cortisol: Hydrocortisone
• Corticosterone

• Regulated by ACTH

• It is the stress hormone and it increases blood pressure, increases blood sugar concentration and it reduces immune function
• It is the main product of the adrenal cortex

• Inner layers of the cortex
• Have darkly acidophlic cells
• Cells are arranged in anastomosing cords. Have less lipid than spongiocytes

• Make and secrete weak Androgens
• DHEA (precursor for Andro)0
• Andro (precursor for Testosterone and Estrogen

• Chromaffin Cells
o Secrete epinephrine OR norepinephrine. No Both
o Stain weakly in H&E but boldly in chromium salts
o Have secretory granules (contain hormone and chromogranins)
• Sympathetic Ganglion Cells

• Controlled by hypothalamus via Splanchnic Nerves
• The release of acetylcholine from preganglionic nerve endings leads to calcium influx causing secretory granules to be released that release the hormones.

• Small gland derived from neuroectoderm
• Secretions are influenced by light/dark cycles
• Invovled in circadian rhythms

• Have pinealocytes
o Produce and secrete melatonin in the dark and secrete serotonin in the light
o Melatonin may regulate cyclic gonadal activity. Melatonin taken up by blood and serotonin taken up by axons
• Have interstitial cells
o Located between the pinealocytes
o Neuroglial like cells

• Concretions which are precipitated by calcium phosphates and calcium carbonates
o They are concentric structures around organic matrix
• Name of concretions is corpora arenacea (brain sand)
• Have unknown function and number fluctutates

• Removes toxic byproducts of metabolism: Urine
• Conserves salts, glucose, proteins and water
• Secretes hormones
• Erythropoeitin, renin, vitamin D3
• Regulates blood pressure, hemodynamics and acid-base balance

• Pair of kidneys
• Pair of ureters
• Bladder
• Urethra

• Large, reddish, bean-shaped
• Retroperitoneal
• Covered by a fibrous capsule

• Three visible structures
• Red dots: renal corpuscles
• Convoluted tubules: cortical labyrinth
• Longitudinal striations: medullary rays

• Functional unit of the kidney
• System of highly elongated tubules
• Modifies initial filtrate
• Made of two parts
• Nephron
o Two types:
• Cortical
• Juxtamedullary
o Has Renal Corpuscle (blood filtering component of nephron)
• Bowman’s capsule –cuplike sac that holds the glomerulus
• Glomerulus- filters the blood to form urine
• Has Podocytes which are cells that wrap around capillaries of the glomerulus via Primary and secondary processes (pedicels) and create filtration slits. Blood is filtered through the slit diaphragms
• Has Mesangial cells- specialized muscle cells that regulate blood flow through capillaries
• Afferent and Efferent Arterioles
• Vascular Pole- where the afferent and efferent arterioles enter Bowman’s capsule
• Urinary Pole- where the proximal convoluted tubule arises
• Has 3 tubules parts associated with it
o Proximal Tubule
• Proximal convoluted tubule
• Straight Part
o Thin Limb of Henle’s Loop
• Descending thin limb
• The loop
• The ascending thin limb
o Distal Tubule
• Straight part
• Distal convoluted tubule
• Has juxtaglomerular apparatus
o Regulates the function of each nephron
• Cells found in the juxtaglomerular apparatus:
o Macula Densa
• Dark spot
• Has tall, narrow, columnar, pale-staining cells
• Densely packed, dark-staining nuclei
• Line the wall of the distal tubule
o Juxtaglomerular Cells
• Modified smooth muscle cells that secrete renin
o Extraglomerular mesangial cells
• Phagocytic cells
• Found near macula dena and vascular pole

Collecting Tubule
• Not part of the nephron
• Made of simple columnar epithelium
• Modifies luminal fluid
• Has three segments:
o Cortical collecting tubules
o Medullary collecting tubules
o Papillary collecting tubules
• Ducts of Bellini

• Regulate solute composition of plasma
• Regulates acid-base balance
o H+ and NH4+
• Regulate body-fluid volume
o Uptake and release of water
• Excrete detoxified endproducts of metabolism
o In the form of urea
• Regulate urine osmolarity
o Concentrates or dilutes
• Secrete hormones
o Renin, erythropoietin, medullipin and prostaglandins
• Regulate blood pressure
• Helps convert Vitamin D3 to dihydro-cholecalciferol
o Controls calcium excretion

• A decrease in blood pressure leads to the following events
o Decreased glomerular filtration rate
o Decreased sodium concentration in fluid of DCT
o Macula Densa is stimulated (osmoreceptors)
o Juxtaglomerular cells are stimulated (mechanoreceptors)
o Renin is released
• Once renin is released it enters the plasma and causes angiotensinogen to be converted to angiotensin I which is converted to angiotensin II
• Angiotensin II will lead to the following events:
o Constriction of peripheral blood vessel
o Aldosterone released from adrenal cortex and has direct action on renal tubular cells:
• Leads to increased sodium uptake from the DCT which leads to increased water uptake
• ALL events will lead to increased blood pressure

• Filtrate that enters the collecting tubules is hypotonic
• As it passes through the medulla, exposed to increasing osmotic gradient
• W/o vasopressin cells are impermeable to water and the urine remains dilute
• In the presence of vasopressin cells are permeable to water and as the filtrate passes through osmotic gradient water moves passively into the interstitium and the urine becomes concentrated and hypertonic

• What urine passes through before entering ureter.
• Made of transitional epithelium

• Transfer urine from the renal pelvis and bladder
• Lined with transitional epithelium
• Two-layered muscularis
o Inner longitudinal and outer circular
o Third longitudinal layer in distal ureter
o Peristaltic waves moves urine to bladder
• Covered by adventitia

• Lined with transitional epithelium
• Loose, fibroelastic lamina propria
• Three-layered muscularis
o Inner longitudinal
o Middle circular
o Outer longitudinal
• Innervated by both sympathetic and parasympathetic innervation
o Parasympathetic controls Micturition Reflex

• Helps conduct urine from bladder to outside
o Makes semen in males
• 2 layered muscularis
• External sphincter of skeletal muscle provides some voluntary control
• Female urethra
o Stratified squamous nonkeratinized with patches of pseudostratified columnar

• Prostatic Urethra
o Transitional epithelium
• Membranous Urethra
o Pseudostratified columnar or stratified columnar
• Penile Urethra
o Pseudostratified columnar or stratified columnar