Paracrine signaling

Juxtacrine signaling

Direct transmission of signal between cells via gap junctions

Epithelial: mesenchymal interations

Epithelial: epithelial interations

Inducer intities

Responder responds: must be competent to respond

Cross-talk: required for each to continue process

1. diffusible proteins trave short distances to target cell

2.bind to specific targetvia receptor molecules

3. act via signal transduction pathways

4.ultimate intracellular target is transcription factor.

5.transcription factors activates or inhibits specific gene expression

6. families of paracrine signaling molecules

FGF- Fibroblast Growth Factor

Wnt- related to Drosophila wingless

hedgehog

TGFβ- transforming growth factor β

-acts over shorter distances

1.non-diffusible factors

2.protein on cell surface of one cell interacts wih receptor on adjacent cell

3.ligands of extracellular matrix secreted by one cell interact with receptors of adjacent cells

Albinism

Ichthyosis

Hair

Mammary Glands

hypertrichosis: excessive hair; localized or general

atrichia: absencce of hair

polythelia: extra nipples

polymastia: extra breasts

inverted nipple: failure of mammary pit to evert

* form interactions between ectoderm (epidermis) and mesenchyme (dermis)

Hair

Glands

Epidermal contributions (from hair buds)

Dermal contributions

Lanugo

hair shaft

epidermal root sheath

sebaceous glands; secrete oily sebum

dermal root sheath

arrector pili muscle

hair papillae with nerve and blood vessels

Sweat glands

Mammary glands

Eccrine: most common; solid downgrowth from epidermis then canalizes

Apocrine- found mostly in axilla and pubic regions; downgrowth of epidermis in junction with hair formation; duct opens into hair follicle

Mammary ridge: thickened epidermal band from axilla to groin

Mammary buds: in thoracic region of ridge; penetratede dermis to for ducts and glands

Mammary pit: depression in surface epithelium; site of opening of lactiferous ducts at birth

Nipple formed by proliferation of mesenchyme surrounding pit; appeaars postnatally

Epidermis

Dermis

1. Initally single layer of ectoderm

2. two layers during month 2

3.multiple layers develop during second trimester from basal layer

4.melanocytes from neural crest

5.Periderm lost by end of second trimester and definitive layers of epidermis are all present and serve as protective barrier between fetus and amniotic fluid

6. vernix caseosa

1. Corium: upper layer forms dermal papillae; lower part forms reticular dermis

2. from mesoderm

3. from neural crest ectoderm- head and neck

a. trunk

(1) dorsal from dermatomes of somites

(2) lateral and ventral from lateral mesoderm

b.limbs from lateral mesoderm

a. outer covering present at birth

b. secretion from sebaceous glands, degenerating cells and hairs

c. protects skin from amniotic fluid

a. periderm

-flattened, superficial

-during first trimester may take part in exchange of water, sodium and glucose between fetus and amniotic fluid

b. basal (germinative)

-layer that will give rise to additional layers

A. mesenchyme

B. paraxial mesoderm

C.somatic mesoderm

D. neural crest

E. types of bone formation

*embryonic connective tissue*

1. pluripotent cells

2. may come from a variety of sources

(a) most from mesoderm

(b) from nerual crest (ectoderm)

*somitomeres and somites*

a. segmentation of paraxial mesoderm; during third week

b. develop in rostral-caudal direction for 2-3 weeks; total of 42-44 pair

c. subdivisions

(1) sclerotome: bone (vertebrae)

(2) dermatome: dermis of the skin

(3) myotome: skeletal muscle

1. Intramembranous: flat bones of head and face

2. Endochondral: most of skeleton; cartilage model

A. Neurocranium

B.Viscerocranium

1. Vault

2.Base

*by intramembranous ossification

a. mostly from neural crest mesenchyme

b. flat bones separated by connective tissue sutures (frontanelles)

c. frontal, parietal and part of occipital bones

*by endochondral ossification

a. neural crest and paraxial mesoderm (somitomeres)

b.separate cartilages that fuse

c. ethmoid, sphenoid, base of occipital, and petrous portion of temporal bone

*by intramembranous ossification

1. neural crest

2. pharyngeal arches I and II

a. arch I: maxilla, mandible, nasal, zygomatic, and squamous portion of temporal bone; malleus and incus

b. arch II: stapes and styloid process of temporal bone

A. Vertebral column

B. Ribs

*form from costal processes of thoracic vertebra

C. Sternum

*from somatic mesoderm of ventral body wall

1. vertebral body from 4 half-sclerotomes

-shifts location of muscle, nerve and blood vessel in relation to segmented structure

2. notochord persists between vertebra as nucleus pulposous of intervertebral disc

A. somati mesoderm (lateral plate)

B. apical ectodermal ridge (AER)

C. fattened hand plate and foot plate at ~week 6

D. axes of patterning limb

E. bones form by endochondral development

F. lower limb lags 2-3 days behind development of upper limb

G.rotation of limbs

1. upper rotates 90° laterally

2.lower rotates 90° medially

1. cartilage appears week 6

2. ossification begins during week 7

1. AER- proximo/distal axis

2.ZPA- anterior (cranial)/ posterior (caudal) axis

3.wnt/engrailed- dorsal ventral axis

1. digital rays: formed by end of week 6; AER confined to tips of rays

2.intervening regions undergo apoptosis (programmed cell death) to form digits

3.ZPA (zone of polarizing activity) at caudal tip of plate determines order of digits

1. essential for limb outgrowth

2.Ineracts with mesoderm to form structures along proximal/distal axis

3.may act as a "clock" for mesoderm

4.maintains underlying mesoderm in undifferentiated highly mitotic state

1. begins at the end of week 4

2. morphogenesis complete by end of week 8

Skull

Vertebrae

Limbs

General

1. cranioscchisis: cranial vault incomplete; anencephaly

2.craniosynostosis: premature closure of sutures

3.microcephaly: small skull due to failure of brain to grow

1. Klippel-Feil syndrome: reduced number of cervical vertebrae; others fused or abnormal

2.spina bifida occulata (cleft vertebra): vertebral arches do not form

3.spinal bifida cystica: accompanied by spinal cord anomalies

4. hemivertebra: congenital scoliosis

1. Amelia: lack of limbs

2. polydactyly: extra digits

3.syndactyly: fused digits

4.club foot: foot adducted and plantar flexed; often accompanied by syndactyly; more frequent in males

5.congenital hip dislocation: underdevelopment of acetabulum and head of femur; more frequent in females

achondroplasia

a.abnormal cartiage formation

b.disrupts epiphyseal plates

c.dwarfism, short extremities

d.hereditary, autosomal dominant

A. Maternal: functional layer of endometrium

B. Fetal: trophoblast and especially extraembryonic mesoderm (chorionic plate)

Primary: trophoblast cell ~day 13

Secondary: core of mesoderm ~day 16

Tertiary: develop blood vessels in mesoderm (chorionic plate)

1. support- rigid framework

2.protection

3.body movement- levers

4. provide an anchoring point for muscles

5.calcium/phosphorous metabolism

6.hematopoiesis

1. long bones

2. short bones

3. flat bones- cranial bones, ribs, scapula

4.irregular bones- vertebra

5.accessory bones

6.wormian bones- aka sutrual bones

Methods of ossification

1. intramembranous

2.Endochondral

-ossification begns in membranes (sheets of connective tissue- 'membrane bones")

a. mandible

b.clavicles

c.bones of the skull- neurocranium and viscerocranium

-ossification occurs within a preexisting hyaline cartilanginous model

-"chondrogenic bones"

-long,short and irregular bones

Viscrocranium- bones of the face

-develop by intrmembranous ossification

-Sphenoid bone :endochodral

-Portion of occipital bone- base of occiput

-Ethmoid bone: endochondral

-Portion of temporal bone: petrous: endochondral

1.hematopoieses

2.calcium storage and release

-Function of Calcium

-Control of Calcium levels in the blood

-blood clotting

-nerve transmission

-muscle contraction

-bone

-kidney

-parathyroid glands

-diet/GIT

-hypocalcemia- tetany: muscle spasms (lock jaw)

-pH is proportional to HCO₃/CO₂

-hypercalcemia

-calcium, phosphorous, magnesium

-Vitamin D: absorption of Ca

-Vitamin A: osteoblast function

-Vitamin C: necessary for osteoid synthesis

-Protein

The Axial Skeleton

-The skull: 22 bones (cranial and facial bones) excluding the auditory ossicles

-Auditory Ossicles: 6 bones total

-Hyoid bone: located above the larynx

-Vertebral column: 26 bones in the adult

-Ribcage/ sternum

-Pectoral Girdle: scapula and clavicles

~cingulum membri

-Upper extremities: humerus, radius, ulna, carpal bones, metacarpals and phalanges

-Pelvic Girdle: 2 ossa coxae

~cingulum membri inferioris

-Lower extremitiies: femur, tibia, fibula, tarsal bones, metatarsals and phalanges

a. calvaria

b. cranial fossa

Cranial bones

1. cranial cavity

2. cranium

a. cranial bones (8)

b.facial bones (14)

*14 bones not in contact with the brain*

-all paired except for vomer and mandible

-AKA viscerocranium

1. Paired

-temporal bone

-parietal bone

2. unpaired

-frontal bone

-occipital bone

-sphenoid bone

-ethmoid bone

1. paired

-nasal bones

-palatine bones

-lacrimal bones

-zygomatic bones

-maxillae

-inferior nasal conchae

2.unpaired

-vomer bone

-Anterior: Frontal, closes by 18-24 mo. (last to close)

-becomes bregma

-Posterior: Occipital, closes by 2 months ( first to close)

-becomes lambda

-Anterolateral: Sphenoidal, closes by 3 months

-becomes pterion

-Posterolateral: Mastoid, closes by 1 year

-becomes asterion

Saggital

Coronal

Squamous

Metopic

Lambdoidal