WARM UP 11/17 1. Write 5 main things that you learned from Ch 3 on the cells. 2. What is a tissue? 3. When do you believe life starts? At fertilization, when the brain forms, when the heart starts to beat? or after birth? 4. Have you ever heard of stem cells? What are they? 5. Do you know what in vitro fertilization is?

NOTES CH 4 11/17 Tissue Intro

TISSUE – group of similar cells working together HISTOLOGY – the study of tissue 4 MAIN TYPES OF TISSUE: 1. Epithelial 2. Connective 3. Muscle 4. Nervous

Tissue formation STEP 1: fertilization creates a ZYGOTE 1 CELL 1 CELL

STEP 2: Cells divide by mitosis

ZYGOTE STEP 3: Hollow balls of cells formed – blastocyst ( days)

What are special about the blastocyst cells? The have not become any special cells in the body yet – they will end up developing into our 220 different cells

What are stem cells? WHAT ARE STEM CELLS? Stem cells are unspecialized cells that are thought to be able to reproduce themselves indefinitely and, under the right conditions, to develop into mature cells, e.g., nerve, skin, pancreas, with specialized functions. They are found in embryos at very early stages of development (see figure) and in some adult organs, e.g., bone marrow and brain.

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STEP 4: blastocyst cells move and differentiate into 3 germ layers – called GASTRULATION At about 2 months

3 PRIMARY GERM LAYERS: 1. Ectoderm 1. Ectoderm 2. Mesoderm 2. Mesoderm 3. Endoderm 3. Endoderm

ECTODERM MESODERM ENDODERM

ECTODERM Outer germ layer These cells develop into tissues of the: Nervous system (brain and nerves) Nervous system (brain and nerves) Integumentary (outer skin, hair, nails) Integumentary (outer skin, hair, nails) Senses (nose, ears, eyes) Senses (nose, ears, eyes)

MESODERM Middle germ layer Cells develop into tissues of the: Skeletal system (bones and cartilage) Skeletal system (bones and cartilage) Muscular system Muscular system Circulatory system (blood, vessels) Circulatory system (blood, vessels) Excretory system Excretory system Reproductive system Reproductive system Inner layer of skin Inner layer of skin Connective tissue Connective tissue

ENDODERM Inner germ layer Cells develop into tissues of the: Digestive tract Digestive tract Respiratory system Respiratory system Glands Glands

These three layers develop into the different cells and tissues of our body, but scientists do not know exactly how one cell become a skin cell and one becomes a brain cell….

STEM CELL ASSIGNMENT