Human Body Plans

Best-Laid (Body) Plans

• The human body consists of about two trillion cells assembled precisely and exists in three dimensions

Basic Architecture

• The head is on top, the spinal cord is toward the back, the guts are on the belly side, and arms and legs are on the sides
• This architecture distinguishes humans from primitive creatures organized as clumps or disks of cells
• This design, featuring front/back, top/bottom, and left/right symmetry, is shared by fish, lizards, and cows

Characteristics

• Front ends possess heads with sense organs and brains
• Spinal cords run along the back
• Anuses are located opposite the mouth at the other end of the body
• Heads are at the forward end, facilitating movement in the direction of travel

Body Plans in Primitive Animals

• It is difficult to find a basic design in primitive animals such as jellyfish
• Jellyfish cells are organized into disks with a top and bottom, lacking a front and back, head, tail, left, and right

Comparing Body Plans

• To compare ourselves with primitive animals, we need tools, just as with heads and limbs
• Our history is written within our development from egg to adult
• Embryos hold clues to life's mysteries and can also derail plans

The Common Plan: Comparing Embryos

• Graduate studies shifted from fossil mammals to fish and amphibians due to embryo research
• Embryos from salamanders, fish, and chicken eggs appeared as whitish cells under a microscope, no more than an eighth of an inch long

Development Process

• Development progress was exciting with the embryo enlarging as the yolk decreased
• By the time the yolk disappears, the embryo hatches

Embryonic Similarities

• Fish, amphibian, and chicken embryos display general similarities
• Head with gill arches
• A little brain that began its development with three swellings
• Little limb buds
• Limbs like bird wings and frog legs looked very similar during their development

Significance

• These observations revealed a common architecture among species
• Differences among mammals, birds, amphibians, and fish pale in comparison to their fundamental similarities in the embryonic stage
• Karl Ernst von Baer's work was recognized in the discipline

Karl Ernst Von Baer

• In the 1800s, philosophers like Karl Ernst von Baer looked to embryos to find a common life plan
• Born into a noble family, von Baer initially trained as a physician
• His mentor advised studying chicken development to understand how organs develop

Pander's Contribution

• Christian Pander, an affluent friend, supported von Baer's experiments due to von Baer's lack of funds
• As they looked at embryos, they found something fundamental which was tracing all organs in the chicken to one of three layers of tissue in the developing embryo
• These three layers became known as the germ layers

Three Germ Layers Importance

• Pander's three layers gave Von Baer the means to ask important questions like
• Do all animals share this pattern?
• Are hearts, lungs and muscles of all animals derived from these layers?
• Do the same layers develop into the same organs in different species?

Comparative Analysis

• Von Baer compared Pander's chicken embryo layers with fish, reptiles, and mammals
• Every animal organ originated in one of these three layers
• The three layers formed the same structures in every species, with each layer giving rise to specific organs

Embryonic Development

• Tiny embryos of all species go through the same development stages
• Fertilization triggers major changes in the egg, with the sperm and egg fusing and the egg dividing to form a ball of cells
• In humans, a single-cell body divides four times over five days, forming a ball of sixteen cells, also known as the blastocyst
• The blastocyst resembles a fluid-filled balloon with no apparent body plan at this stage

Implantation

• Around the sixth day post-conception, the cell ball attaches to the mother's uterus, initiating a connection for bloodstream sharing
• There remains no evidence of a body plan
• If implantation occurs in the wrong place (ectopic implantation), like the uterine tubes, serious and dangerous results may occur

Ectopic Pregnancy

• 96% of ectopic implantations occur in the uterine tubes near the conception site, often due to mucus blockage
• Ectopic pregnancy can cause tissue rupture if not addressed promptly
• In rare instances, the blastocyst may be expelled into the mother's abdomen or implant on the rectum or uterus lining, possibly resulting in a full-term fetus

Development Stages

• During the second week post-conception, the blastocyst implants with part embedded in the uterine wall and the rest free
• The flattened disk that develops becomes the human embryo, forming the entire body from the top part of the ball
• The part of the blastocyst below the disk covers the yolk, resembling a two-layered Frisbee

Germ Layers

• The oval Frisbee transforms into Von Baer's three germ layers, resembling a human as cells divide and tissues fold
• Eventually, tissues move and fold, forming a tube with a swelling at the head end and another at the tail
• Cross-section reveals a tube-within-a-tube structure, with the outer and inner tubes being the body wall and digestive tract, respectively

Layer Derivations

• The three layers are named based on their position
  • The outer layer is the ectoderm
  • The inner layer is the endoderm
  • The middle layer is the mesoderm
• Ectoderm: outer body parts and nervous system formation
• Endoderm: inner body structure, including digestive tract and glands formation
• Mesoderm: tissue in between the guts and skin, including much of the skeleton and muscles formation
• Regardless of the species, all organs form from the endoderm, ectoderm, and mesoderm

Embryonic Features

• Early days are characterized by transformation, going from a cell to a ball of cells and ending up as a tube
• Von Baer revealed that embryos have fundamental life patterns
• Features are shared by every species and those that vary from species to species

Shared Features

• Shared features, like tube-within-a-tube arrangement, appear relatively early in development for all animals with a backbone
• Distinctive features, such as larger brains in humans, shells on turtles, and feathers on birds, arise later

Comparing Embryos

• Von Baer compared embryos and noted that the embryos of different species looked more similar than do the adults
• Ernst Haeckel's "ontogeny recapitulates phylogeny" approach claimed each species tracked evolutionary history through development
• The embryo of a human went through a fish, reptile, and mammal stage

Relevance

• Comparing embryos of one species to embryos of another uncovers evolution's mechanisms and is more meaningful
• Embryos of different species are not completely identical, but are profoundly similar
• All have gill arches, notochords, and a tube within a tube structure
• Embryos, including fish and people, share Pander and von Baer's three germ layers

Organ Development

• At four weeks post-conception, the embryo is a tube within a tube, with three germ layers giving rise to all organs
• This raises questions about how the embryo "knows" to develop a head at the front and an anus at the back
• Unclear what mechanisms drive development and enable cells and tissues to form bodies

Embryo Investigation

• To answer these questions, a new analytical approach was required, rather than comparing embryos
• Embryos were chopped, grafted, split, and treated with chemicals to study their development

Experimenting with Embryos

• Biologists at the turn of the twentieth century questioned where the information lies to build bodies
• In 1903, German embryologist Hans Spemann investigated how cells learned to build bodies during development to determine body-building information location

Spemann's Experiment

• Working with newt eggs, Spemann devised an experiment
• He pinched one side off from the other using his daughter's hair as a lasso loop
• The embryo formed twins as two complete salamanders emerged, each viable with a normal body plan

Mangold's Work

• In the 1920s, Hilde Mangold worked with small embryos in Spemann's laboratory
• Her fine control helped conduct demanding experiments
• A salamander embryo is a sphere about a sixteenth of an inch in diameter
• She transplanted a small piece of tissue from one embryo to another
• Transferred an area where cells were to form much of the three germ layers
• The grafted patch led to a whole new body formation, including a spinal cord, back, belly, an even a head

Mangold's Discovery

• By moving a small patch of tissue in the embryo, Mangold produced twins
• She discovered a tiny tissue patch able to direct other cells to form an entire body plan
• The incredibly important patch of tissue was known as the Organizer

Acknowledgment

• Mangold's dissertation work was to win the Nobel Prize, but she died
• Spemann won the Nobel Prize in Medicine in 1935 for "his discovery of the Organizer and its effect in embryonic development."
• Scientists consider Mangold's work the single most important experiment in embryology

Vogt's Contribution

• Simultaneously with Mangold, W. Vogt designed techniques to label cells, allowing experimenters to watch egg development
• Vogt created a map of the embryo showing where every organ originates in the egg

Mapping Bodies

• From the early embryologists, specifically von Baer, Pander, Mangold, and Spemann, all the adult body parts can be mapped to individual batches of cells in the three-layered Frisbee
• The general body structure are initiated by the Organizer region discovered in Mangold and Spemann's experiments
• All mammals, birds, amphibians, and fish have Organizers
• It's sometimes possible to swap one species' Organizer for another, for example grafting the Organizer region from a chicken to a salamander embryo yields a twinned salamander

Molecular Basis Of Organizers

• Organizers contain DNA which has instructions for building bodies
• Von Baer observed embryo development and fundamental patterns in bodies
• Mangold and Spemann physically distorted embryos to learn how the tissues build bodies

Genetic Investigation

• By using DNA, insights into our genetic makeup can occur by answering questions about our genes controlling the development of our tissues and our bodies
• Flies mutations are important clues to the major body plan genes active in human embryos

Body Plans In Flies

• Flies have a body plan with a front and back, a top and bottom
• Their antennae, wings, and other appendages pop out of the body in the right place
• Mutant flies can have limbs growing out of their heads or have duplicate wings and extra body segments
• Studying abnormal flies has been occurring for over one hundred years

Observations Of Mutant Flies

• Mutant flies had organs in the wrong places or missing body segments
• DNA errors cause the mutations
• By visualizing the chromosome and breeding mutants, the chromosome responsible for the mutant effect can be identified

Mutation Analysis

• Comparing genes of individuals with the mutations to those without pinpoints the responsible region and stretch of chromosome
• A fly has eight genes to make such mutants that lie next to each other on one of the long DNA strands
• Genes that affect the head segments lie next to those that affect the segments in the body

DNA Structure

• Mike Levine, Bill McGinnis, and Matt Scott noticed a short DNA sequence virtually identical in each species in the middle of each gene
• This sequence is called a homeobox
• The eight genes that contain the homeobox are called Hox genes

Hox Genes

• Versions of Hox genes appear in every animal with a body
• Activity of a gene matches its position on the DNA in flies and in people
• Genes active in the head lie at one end, those in the tail at another, with genes affecting the middle of the body lying in between
• Versions of the same genes sculpt the front-to-back organization of the bodies

Hox Gene Effects

• Mess with the Hox genes and you mess with the body plan in predictable ways
• Lacking a gene active in a middle segment in a fly can result in the midsection being missing or altered
• Hox genes establish proportions of our bodies and are involved in the development of individual organs

Hox Gene Composition

• Different creatures have different numbers of Hox genes
  • Insects have eight
  • Mammals have thirty-nine
• Mammalian Hox genes arose from a smaller number of genes in the fly

Understanding The Organizer

• Despite differences, mouse genes are active from front to back in a very precise order
• The Organizer in Science was viewed as little more than a curiosity by the 1970s
• The discovery of Hox genes in the 80s changed everything

Robertis Laboratory

• In the early 1990s, Eddie De Robertis's laboratory at UCLA looked for Hox genes in frogs using Levine and McGinnis's techniques
• They found several genes, including one that was active at the site that contains the Organizer at the time of development
• They were looking at the Organizer, and there a gene seemed specifically to control it or be linked to its activity in the embryo

Organizer Genes

• Organizer genes were identified in labs
• Another gene was found by Richard Harland at Berkeley, which he called Noggin
• Taking some Noggin placed in the right place in an embryo functioned exactly like the Organizer as the embryo developed two body axes, which means two heads

Genetics

• De Robertis's gene and Noggin are DNA, that make up the Organizer
• Genes interact to organize the body plan and can play different roles during development
• New tools mean gene function can be understood by knowing how genes interact to build cells, tissues, and bodies

Gene Behavior

• Genes interact with each other
• A gene may inhibit or promote
• Genes can turn another gene on or off with interactions
• Genes shed light on the mechanisms that build bodies

Noggin

• Noggin does not instruct any cell in the embryo about its position but acts with other genes
• Another gene, BMP-4, is a bottom gene turned on in cells that make the bottom of an embryo
• Noggin does not allow cells to develop as 'cells on the top of the body' instead, it turns off the signal that would make them bottom cells

Axes Of Animal Bodies

• Most animals have body axes defined by their direction of movement relative to mouth and anus
• Mouth and anus orientation is reversed in jellyfish, corals, and sea anemones
• These creatures have a mouth, but no anus. That opening is used to expel waste
• Biologists were analyzing this group of animals: sea anemones due to primitive body structure and relatedness to jellyfish

Sea Anemones

• Sea anemones, shaped like a tree trunk, have a long central stump, a bunch of tentacles at the end, a front and back, a top and a bottom
• The oral-aboral axis is line from the mouth to the base
• Martindale and his colleagues found that their head-to-anus axis-determining genes is in the sea anemone active along the oral-aboral axis

Other Axes

• Sea anemones don't compare to our belly-to-back axis
• Belly-to-back genes were uncovered in the sea anemone, but the axis did not correlate with the animal's organ arrangement
• Jellyfish relatives such as sea anemones have a body plan like us with a front and a back by the same genes versions

Directive Axis

• The directive axis defines two sides of the creature, almost a left and right, and in sea anemone embryos, a version of Noggin is turned on at one end

Common Genetic Recipes

• Inject a frog egg with extra amounts of frog Noggin, and the frog will grow extra back structures, sometimes a second head
• Take the product of Noggin from a sea anemone and inject it into a a frog egg
• There will also be a frog with extra back structures

Adventures in Bodybuilding

• Graduate career involved microscopy to understand bone formation
• The limbs of salamanders or frogs were stained, cartilage dyed blue, and bones dyed red
• Tissues were cleared with glycerin

Development Process

• During microscopy, the animal was observed being built
• The earliest embryos would have tiny little limb buds
• Inside would be evenly spaced. Clumping inside the limb bud occurs at a later stage
• Cells would adopt different shapes and the bones would form
• Each of the clumps seen during the early stages became a bone

Complexity Of The Body

• A limb is built by small pieces joining
• Houses have builders, limbs and bodies do not
• Limb-building information is contained in each cell

Body Composition

• Much of a body is locked inside the cell
• Bodily uniqueness stems from the attachment structure of its cells
• A way to make a body in the first place has to be established
• Cooperation is needed from cells to make tissues and structures

Essence Of Life

• Cells have to cooperate to come together to make a new kind of individual
• Not every clump of cells can be awarded the honor of being called a body

Distinctions Between Cells

• A mat of bacteria or a group of skin cells is not the same as an individual
• If removing some bacteria from a mat means the remainder will be smaller
• If we remove some cells of a human or fish, you could end up with a dead human or fish

Feature Of Bodies

• The component parts work together to make a greater whole and not all parts of bodies are equal
• There exists a division of labor between parts
• Brains, hearts, and stomachs have distinct functions that include the cells, genes, and proteins

Features Of A Body

• The body has an identity that other parts-organs, tissues, and cells-lack
• Our skin cells continually dividing and dying
• Yet you were the same person seven years ago
• We remain the same individuals despite continual change

Homeostasis

• Each of our organs knows its size and place in the body
• We grow in the correct proportions because our arm bones are coordinated
• Bones in our fingers and our skulls have coordinated bone growth
• Cells maintain integrity and the regularity of the surface
• Cells inside a wart do not know to stop growing.
• Finely tuned balance is needed to prevent bodily disruptions as the individual creature can die

Cancer

• A cancerous tumor is born when batches of cells no longer cooperate with each other, by dividing endlessly, or by failing to die
• Cancers behave best in their own interest until they kill the human body
• Utilization of new mechanisms occurred to work together

Cellular Communication

• Need to be able to stick in new ways
• Molecules are needed to make our organs distinct
• Shift from single-celled animals to animals with bodies revealed tool invention
• New creatures developed new organs that helped them sense, eat, and digest their world

Origins Of Body

• Most of life's history is the story of single-celled creatures.
• Animals with hands, heads, sense organs, even body plans have been around for only a small fraction of the earth's history
• We are after the when, how, and why of bodies. The Precambrian discoveries tell us the when

Evidence Of Body

• Our bodies are linked with Precambrian disks, fronds, and ribbons
• What are our bodies possible: no different from Gurich's and Sprigg's ancient impressions
• The scaffolding of our entire body originated in single-celled animals

How A Body Is Formed

• Creatures have glue which is astoundingly complicated
• Glue holds our cells together and form communication
• Glue is a variety of different molecules that lie between our cells
• The glue is microscopically giving each of our tissues and organs its distinctive appearance and function
• The eyeball and femur will look different on a microscope

Importance of Organs

• Tissues have all kinds of different cells, with different kinds
• Organs have strips or columns of cells
• Some regions have strips or columns of cells and some are loosely attached
• Some areas, where cells are loosely packed, are filled with materials that give each tissue in a certain physical properties

Skeleton

• Focus on the skeleton to learn about molecular structures
• Without skeletons, we would be masses of goo
• Skeletons make the basic biology and behaviour of the human being possible
• Skeleton analogy of a bridge relies on the microscopic properties of its made from

Skeleton Strength Through Composition

• Strength is based on sizes and shapes and is also based on the molecular properties of our bones
• When muscles contract, our feet push against the ground to move us
• Design matches with functions; and high jumper is different bone proportions sumo wrestler

Bone Features

• Bone distinctive mechanical properties consists of Bone cells are highly organized in places
• Strength of bones between between separated cells rely on materials
• The one mineral is called hydroxyapatite which we discussed in Chapter 4
• Bones are shaped to maximize compressive and minimize twisting and bending
• Collagen is another molecule in our bone cells that has mechanical and pulling, but it collapses

Bone Tissue

• Tissue relies on cells which sits in a sea of materials such as collagen and hydroxyapatite
• Cartilage is another tissue in our skeleton and its properties rely in its microscopic structure
• Cartilage is another kind of molecule one of the most extraordinary
• A proteoglycan complex, gives cartilage strength when squeezed or compressed, Shaped like a giant three-dimensional brush
  • Proteogycan: molecule that swells up with water
• Collagen fills cells for cartilage cells
• Ratios among materials define the mechanical differences
• Hydroxyapatite and collagen are the most prominent materials as lots of proteoglycan

Origins

• Our body has One property is common among animals, regardless whether there is a skeleton or not is a cell
• These cells are held by collagen
• Collagen accounts for 90 per cent of the protein

Cellular Attachments

• Cells need to stick together and talk and each cell needs to know how to attach by molecular rivets
• Some bind like contact cement, others bind selectively, only the same kind if a rivet
• Selectivity aids ability to organize bodies which create bone cells, skin to skin, and so on

Cell Organization

• Cells need to know how to behave which is division, molecuke production adn death
• Communication creates molecule 'words' between the cells
• The molecular signal sets of reactions that all the from the outer molecules to the nucleus which cause genes

Making Bodies Possible

• All bodies require structural components like collagens and proteoglycans, molecular rivets that hold cells and the tool to communicate
• The the tools in animals that build animal are used in single celled animal
• How these tool used in single-celled but doesn't build bodies?

Cellular Similarities

• First look to compare animal and microbial genomes
• Earlier animal and microbial genomes comparisons are not present. In many cases the adhesive factors are not the in the single animal
• Genes unite to make bodies arose with the tools
• A story about genomes has Nicole King doing a study using chaonoflogellates which is closest ancestors
• The Human Genome aided in searching genes through gene mapping tools and other project through sequencings
• A reason is these new genes help in many different species
• One finding Is that the look very spongy with gobiet similar to the bodies
• These were degenerate sponges without other things
• So what could be do different in the body than a sponge look at
• It look exactly other microbes and sponges DNA
• The genetics of cells also came together, in animals they were active
• Molecules and matrix of cells and the cellular ferry all of the components are on of the cells
• This is a connection and hold of these together
• Collagens are pressent adn

How Bodies Are Formed

• To solve why 3.5 by has no body requires fossils, a sudden in millions
• Over night they appear this takes it faces
• The potential building bodies was ever
• One theory with a lot bodies with cell avoids getting eaten
• Defense
• The interplay has led to body building molecule

Microbe Eating

• Microbes often engage by attaching eating other microbes and often use lures
• These are similar to our own cells exchange
• The predation from bodies shows what Martin said
• He placed algae into it with the
• Algae respond with it in less than with two hundred

Predator-Prey Relationships

• Number reduce to all in eight
• So that it can survive
• Then the were removed
• This led the algae to the same to 8 algae

How Can Organisms Form?

• Now the with cell had was the alage
• All of could in the year it why more sooner

Origin of Bodies

• The and in
• bodies

Costs Of Building Bodie

• Eat small animals
• more control better
• A lot of oxygen
• a synthesis need to meet to the metabolic elements in

In The Atmostphere

• Atmosphere
• The level the billion increase had since
• Did in rocks
• In of a perfect storm to begin in that

Oxygen And Creation Of Organs

• Took molecular tool
• The building could get food, why
• that has